NL 5/10...Folding Set And It's Not Close

[Lucky]

Doing this from memory. Good online full NL 5/10. 2 donks reallly spewing chips. Villian seems solid, (18/6/3) probably views me similarly. I have 2300. villain has 4k.

On to hand. Donk limps in (Got half in with slick earlier, nothing on flop, got other half in to double my AA). Villian limps. I limp on button with 33.

Flop is 3 6 9 rainbow. Donk bets 100 (This could be anything, probably overcards). Villian Calls. I raise to 300 (I want to get donk HU, if he's got a set, Ill pay him, but i can probably take his 1k).

Anyway, Donk folds. Villian raises up to, like 3k. I, of course muck. I'm positive he hit set.

It looks like he put me on set and figured I'd pay off his higher set. With that monster bet? Does anyone else play a set this way ever? In his shoes, against an opponent on the tight side at a full table. I'll call the raise, then check raise the turn.