It does not!

… What about an index?

Here's one! It's divided by summoner.

Is there a clear subdivision for it under High Summoner Gandof?

Newp.

… How big is the relevant section?

Not very! About two dozen pages.

What does it say?

It tells the history of High Summoner Gandof in some detail, but the relevant passage might be this one:

Long ago, fiends known as Qactuars roamed the Djose Continent freely. They ran rampant, ravaging fields and tormenting travellers. Then Lord Gandof appeared. He scoured the continent for the Qactuars and drove them to these plains. Once he'd gathered the Qactuars together, Lord Gandof linked the sign of the fayth, whereupon the Qactuars turned to smoke and were absorbed by a stone. The Qactuars were thus sealed into stone, fated to face lightning day and night. Unless someone again links the fayth sign and releases the seal, they shall suffer within the stone for their deeds. Thus did Lord Gandof bring relief to peoples all over Spira. He believed that the battle with Sin was only one great part of a summoner's greater mission.

… Theo goes over to Kaede with the book. "Apparently it – the cactuar stone thing – stores the Qactuars that used to terrorize the rest of the Djose Continent in the past. And are now fated to lightning."

Rikku comes over and looks at it. "That's wrong. Cactuars aren't really fiends."

"… Is there a difference between the two spellings?"

"Well, I don't think so?" She grabs the book and leafs through it. "Seems like Qactuars are from Bikanel. Not fiends. Fiends used to be dead people, cactuars bloom in the desert."

"Do they drop spheres when they die? Turn into pyreflies, don't leave a corpse, that sort of thing?"

"They do leave a corpse."

"… So they're more just like monsters? Instead of actual fiends with all the other flourishes?"

"No, they're like people—they have a society and everything."

"Sapient? Or just a reasonably smart animal?"

"Some Al Bhed know how to speak their language."

"They have a language?"

"Yeah! It sounds like squeaking."

"– Do they, did they actually go around terrorizing people or is it going to turn out that this was a war where non-cactuars decided they didn't like their pesky cousins and decided to commit some sort of genocide?"

"I don't know if I'd say they terrorize people but they do attack. When fighting—" A particularly loud lightning strike hits a tower nearby and she yelps. After a couple of seconds she continues, shaking: "F-fighting c-cactuars you d-d-don't usually kill them, though, that'd be evil."

"… I'm a bit confused by everyone just ignoring the fact they're unlike other fiends and just going ahead and calling them fiends anyway? And – there are more just blooming in the desert, so – were they just all over before, and this guy rounded them up, and they don't care about the others?"

"I'm not sure? This was hundreds of years ago. Cactuars and humans don't really see eye to eye on the island, but Dad's been trying to get some cooperation going and it's been alright."