Huge River Overbet from a total rock

[JustPlayingSmart]

2/5 NL at Windstar in Oklahoma. Terrible game. I have $600 in front of me. Villain has approximately $2500, and since I've only been here 30 minutes I have no idea how he got it. Every pot is raised and heads up, so I'm playing like a rock and hating it. I bluff check/raised with an underpair to get above the $500 starting stack, but villain wasn't there for that.

He raises to $20 in EMP and I call with 9s7s. Everyone else folds.

Flop is 8s 5c 4c. He checks and I check.

Turn is As. He checks and I bet $40. He calls.

River is 8d. He bets $80, and I move in for almost $500 more.

Flame me.

P.S. In case anyone didn't realize, I'm the rock.