We don't think this looks like a slightly unconvincing attempt to bluff the scare card?

It looks to me like he's trying a little bit too hard to rep a flush. Its an insta pot+ bet - if he was looking for value wouldn't he take a little more time to decide how much we might be willing to pay off? Maybe he instead made up his mind when we called the turn that we would have included flush draws in his range and he would therefore barrel any diamond on the river. His earlier streets don't really look that much like a flush draw to me, but could probably be construed as one, especially as he cbets less than most.

I dunno, I play well below these stakes and you guys are a lot better than me, but in my games I would think it reasonably likely that he's trying to push me off with Ax or KQ or something like that, and it only needs to be the case ~35% of the time to call this (this obv goes up a bit if we think a shove is better because we think it will make him fold AQ and weak two pair type hands).

If I'm way off, please tell me why. I'm keen to learn.