From my experience, this flop bet/call looks a lot like a flush draw trying to give themselves a cheap price to a turn, or a weak ace trying to see where they are at.
Just because he doesn't bet or raise the turn doesn't change anything. Since the board paired he might think putting in a bet or raise would be overplaying his flush if he put you on an Ace, twopair, or a set.
The river looks like a blocking bet for the same reason, with a small Ace or a flush.
And of course there's the rare wierdly played monster or weaker hand.
But below are some ranges to give you an idea of how often he'd have each hand on each street.
Given this, trips appear most likely, but I don't think many people would call a large raise on this river with trips. Especially since so many of his trips have weak kickers. And since he's unlikely to 3bet with a flush since he's scared of a full house, I'd make a smallish raise to like 50 or 60 and fold to a shove. I think that's the best play. You get looked up by most of his trips. Since almost 30% of his range beats you, you need to get called by about half of his range that you beat for a raise to be correct.