They are older than the Elves (maybe as old as the universe? They claim to be but it's hard to know for sure; the Elves could claim to be gods to some species out there and they'd probably be believed). They are very powerful (maybe magic? Again, hard to tell for sure.) They accidentally wrecked a lot of the planet Elves first lived on so then they invited Elves to Valinor, where they would want for nothing and be taught advanced physics and engineering in exchange for being an extremely well-behaved population. Some Elves took them up on it, and they live in Valinor now, and recently they invented lightleapers and went exploring and found this place.

Gosh. It seems like the difference between magic and not magic is whether they can explain how they do things so you can do them too, do they do that?

Some of the things they do can be explained, but some can't, and some - well, now they can explain to the Elves how they back up the Elves but it certainly seemed like magic back before the Elves had invented computing.

At this time they are interrupted by a squad of grey-haired people who say that on the order of some different senators they're maintaining a perimeter around the aliens everybody shoo. People set about shooing.

The aliens would like to go exploring, actually. Perhaps these new people can accompany them?

No they have to stay here.

Is there some concern?

They just aren't to go wandering about until further notice.

They might get back in their starship and go land somewhere else and explore there, is that all right?

No!

...can the aliens please explain the concern so that the Noldor can evaluate how best to balance it with other concerns like how they have been stuck on this ship for five days and would like to go explore.

They are just doing what the senators so-and-so said and they said the aliens are staying here till further notice.

...the aliens have a discussion about whether to leave anyway. The considerations are that it would be rude to their hosts and might make the hosts nervous; it does not seem to occur to them that the hosts might stop them or attack them. 

...the soldiers explain that they are not allowed to leave.

Yes, but absent any explanation of the reasoning behind this rule and given that the aliens do not seem to understand that they have been stuck on a ship for five days, they might leave even though it is not allowed.

Then they will be stopped.

Why?

Because they're not allowed and if you do things you aren't allowed to do they'll stop you they brought guns.

What are those?

...weapons.

...why did they bring weapons?

So they can stop anybody who does things they are not allowed to do.

...what an alarming approach to stopping people who do things that are not allowed to do! What if they have a good reason, or are confused, or are unwell, or for that matter it's kind of an alarming approach even if they're doing it on purpose for no reason!

They are not here to argue.

Another bunch of greys shows up and is here to argue! With the first batch. They are to stop threatening the aliens! They are to let Soldiers Batch 2 escort them to the capitol!

Aliens agree with Batch 2 because going somewhere sounds nicer than being stuck. Also because threatening people is bad.