The dragons swerve.

It's not that they recognize the guns - Falmart may technically have explosives, but only in the sense that there are some individual people on the continent who dabble in the right kind of magic or alchemy to produce a primitive version of the effect. But their riders do recognize soldiers waiting in ambush, and for all that dath ilani uniforms and armor are strange to their eyes their positioning is unmistakable.

That's not going to work like you hope it will. 

One of the biggest factors in ensuring handheld firearms took longer to get adopted than artillery is that early firearms are terrible. They're expensive to supply, their rate of fire is slow, their accuracy is abysmal, and they have a bad tendency to stop working if they get wet. Compared to a mature technology like the longbow that can cripple a man at several hundred yards if it gets past his armor, it leaves much to be desired. Even in pre-screening dath ilan it took some time for people to change over, though they largely had the foresight to prepare for it ahead of time.

These are not early firearms. They fire heavy steel bullets at over twice the speed of sound, several hundred times a minute at full bore, and if their aim is imperfect it's a sight better than any bow or sling on that score. Hitting the riders is going to be a hard ask, at the speeds they're going and with an entire wyvern between them and the guns, but if they take down their ride that's basically as good and those wide wing membranes are an easy target.

That's fine, those riders were the ones they were trying to keep safe from the attack in the first place - the wyverns are immune to small arms fire.

I don't suppose you can operationalize that?

Dath ilani soldiers will observe the bullets connecting with their targets and skittering off, though someone especially keen eyed might see one of them leave a mark occasionally.

Wyvern scales are harder than steel, thick enough that the bullets won't penetrate, and tightly packed around their body that there's no realistic way for a bullet to get through the gaps. They still transfer the kinetic energy, of course, but the scales are large enough to disperse the force, and these bullets have significantly less force behind them than an attack from a fellow wyvern. It's by no means a pleasant experience, but absent a particularly lucky hit sustained small arms fire will mostly only take down a wyvern slowly by attrition. 

On Falmart, the going strategy for fighting wyverns when you don't have your own wyverns (as is unfortunately common in the empire's civil wars) is to run away, ideally after they are deployed and before they show up on the battlefield. Where that's not an option, they've learned to cope with aiming for the riders.

It's not that they're an easy target - they're armored against that, sometimes even with wyvern scales of their own, and riding on the back of an incredibly swift aerial mount! But their armor has gaps, and underneath it is a distressingly mortal body. Missile fire typically rates second under accidental death on the job, but it'd be a different story if everyone had weapons like these barbarians. Their advantages and quick reaction let them avoid the worst of it, but a number of them are sporting bruises and broken bones and a few of them are now casualties.

Wyvern riders don't like the idea of taking casualties. You could say something about their class interests in not being killed by enemies, but it's as much a matter of pride as self preservation, and whenever a nation's archers pull off a particularly successful defense they rarely live to regret it. They're going to come back in for another approach, but smarter this time.

The soldiers aren't less ready the second time, and for all they're apparently under-gunned for this scenario they aren't idiots. Their aim is better than it was, or at least more directed at the right targets, and they're more ready for the bizarre creatures' speed and flight patterns. And they still can't let them get to the evacuating civilians.

They're not happy about that, and several more of them outright die on the approach despite their own precautions. But then they're close enough to return a little fire of their own, and they intend to replay the favor with gusto. Where dath ilani troops stand alone, teeth and claws and spears tear them to pieces; where they are clustered... their heads rear back as though to spit, and their jaws unhinge to make room as a stream of pressurized liquid makes contact with the oxygen-rich air around. Cones of bright yellow flames wash over hastily-assembled fortifications, and find the makeshift shelters wanting.

Most of them survive it. It's a simple matter of physics; human bodies are largely water, which takes a truly enormous amount of thermal energy to heat appreciably and renders them pretty resistant to outright burning. Fires usually kill people by making them unable to breathe, largely by toxic chemicals released in the burning process, and for all that it's rather impressively hot the breath just doesn't last long enough for it to be an exception to that rule.

That doesn't mean they're in any position to fight, though, not with the horrific burns and choking lungs and vision issues. Civilization might be able to make protective equipment for this sort of danger, but that doesn't mean their soldiers wear it into battle.

The dragon corps will finish them off. These may be barbarians, but they were courageous and fought well; they don't deserve to face the lady below denied even their dignity.

This is probably not them intentionally going out of their way to inflict true death as a threat but that doesn't mean Governance is not very unhappy about it. And for all that biological flamethrower CAS is a deeply bizarre way for another civilization's military technology to develop, it's clearly effective enough that refraining from further escalation is also going to get a lot of dath ilani killed. They're still nervous about the unknown unknowns, like this being somehow a horrific misunderstanding or the possibility of the aliens escalating back again and the resulting fight destroying the city, but they're out of good options and the prediction markets think this way is probably better in expectation.

The order is finally given to scramble the fighter jets, and Schelling Point's inbound logistics grid is diverted towards supplying people already on the ground with heavier equipment. 

For ten minutes, the Saderan Dragon Corps has uncontested control of the city's airspace. They don't know that they're on a specific timer, but even if there weren't more of those ?archers? deployed elsewhere in the city that they'd really like to keep from linking up it probably won't take the locals very long to think of hiding in the buildings. And they're very fast, even if they end up losing a bunch of time at every engagement actually finishing off their enemies. Compared to the earlier cavalry scouts or the masses of infantry slowly spiraling away from the gate, it's a difference of night and day.

It's a bloody harvest. Their guns are good enough to make the dragon corps pay for it, but not good enough to win or drive them off once the invaders know what they’re dealing with. They can’t just hide and wait out the riders either, because where they don’t find soldiers they go after civilians and they aren’t very careful with the heads.

It would be nice to have some kind of agreement not to go for true-killing or noncombatants, and indeed as a matter of principle Civilization is predictably willing to compensate any enemy who gives up strategic advantage thereby, but they were either insufficiently legible about this or their offer wasn’t predictably generous enough to offset whatever strategic advantage the aliens are getting from it. That’s going to go in the failure analysis somewhere, but it’s not really a surprising outcome that that particular area failed; given how mutually destructive wars are, anyone you can negotiate rules of engagement like that with is probably someone you can just negotiate to not fight with in the first place.

Falmart may not have guns, but the idea of the weapon is not beyond their ability to understand. If you told a Saderan general about the existence of a form of missile weapon significantly more capable than slings or arrows, it wouldn't be too much of a leap to realizea thing or two about the effects on warfare, and if they underestimate the extent to which a gun could change warfare they would at least be largely correct about the direction. Having their first introduction to the topic being seeing it in action is rather more of a shock, but it's not a fundemental challenge to their worldview and having seen the results it's not actually that difficult to determine roughly what is going on.

The same cannot be said of other weapon systems. One moment the surroundings are clear, and the next half a dozen wyvern riders are dead and their mounts grievously injured.

How-? Where?

Their fellows scatter, weaving around and looking for whoever or whatever just did that, but they can't see anything-

Low against the horizon, light grey paint jobs blend in near seamlessly with the sky behind. The targets are too unusual and too close to a population center for them to be confident engaging from beyond visual range, but forty kilometers is a long way spot something from when you don't even know what you're looking for.

...According to people relaying information from the close in camera feeds, air-to-air missiles aren't reliably dropping the (presumably absurdly bioengineered?) creatures without a direct hit. They're killing the riders, but that's still very concerning.