I would expect my opponent to 4bet QQ+/AK and possibly AQ, so we can remove them from their range, but believe it or not, it is fine for MP to flat a BB 3bet with hands like A5s, 98s, KTs, and even lower suited connectors. Although, looking at some charts, I was surprised that JJ can sometimes flat opens in the BB rather than being a mandatory 3bet as it is from any other position.
Betting 10bbs into a 24bb pot means they need 23% equity to call, though the rake makes calling slightly worse. It’s become kind of a common size for my c-bets in 3bet pots because it gets trash to fold, gets some hands that otherwise might fold to continue (like 8x hands on this flop for instance) and doesn’t overly inflate the pot, while still creating a big enough pot for when I want to get stacks in by the river. I wouldn’t call it an information bet (I don’t intentionally bet just to gain information), as I might bet this size with KK or 88. It seems like a good size for my range on a board that maybe favors villain’s range (though I’m not sure that I’m correct in that thinking).
Against some players I’d view the raise on the flop as a way to purely extract value. As in this case, top set can get a lot of value from overpairs on this flop. I wouldn’t say villain was concerned about the flush draw, they were going for value against my strong looking range on a board where they can have draws. Good players will be balanced between bluffs and value, which kind of forces you to continue with overpairs in a low spr spot, while against players who almost only do this for value, it could be a fairly easy fold.
So to answer your final questions, I think villain could definitely have a bunch of Ahxh or other flush draws, straight draws, or combo draws (though I block some) like KhQh, J9, 97, 76 also possibly with hearts. These all make good bluffs. While they might be getting a good price to continue, they don’t have showdown value so they benefit from trying to generate some fold equity by raising. And some players might even just call this flop with sets because they can raise on future streets (though maybe not on this somewhat wet board), and raise mostly as a bluff.