Having read spoon's post, I agree that this could be a tight player scared of the club and then being happy with his overpair at river. That said, nits tend to play overpairs hard and fast, especially when it's a wet flop. At the very least, after we flat the flop, I'd expect a bigger turn bet with an overpair because he knows he's a big favourite against our flop calling range.

But I've seen people taking these kind of lines as bluffs, all too often. The pot size river bet doesn't look like value to me. It looks like he's trying to get us to fold our busted draws. This doesn't look strong to me. I wouldn't be all that surprised to be proven wrong though.