Doesn't look like a set to me. A set would bet the turn trying to protect against the flush draw. I think villain has a weak K or the flush draw and checked the turn to see what you would do. He probably put you on a flush draw once you checked the turn because if you had a hand, why wouldn't you have bet it? So, when the river didn't complete the flush draw, he bet out...

I would have bet 1/2 pot on the turn to see what he does. A raise would clearly say "set"...as played, you can't really tell what his river bet means.