25/50 vs. unknown

[Dale Dough]

OK I didn't have stats on him yet, but the guy is a total unknown to me, and he played 5 hands out of 5 so far that I've been there. He has 7.5k behind, I have like 4700.

4 handed. CO opens 200, Villain calls in SB, I make it 900 with AT. CO folds, Villain calls.

Flop: 873 rainbow
Pot ~2k

Villain leads full pot, 2k. I have 3800 left. WTF? If you say 'fold', what does he have and why would he play it like this?

[dzh90]

seems like a super easy fold, unless you really have reason to believe AT is ahead because I doubt he is going to fold for $1800 more.