Big action on a 1-suited flop

[Toonces]

Well, I'll never know what CO has. Now, it's true that I need to be 93% sure that neither player has a heart flush to call the river. It seems to me that anyone trying to take down the pot would be 3-betting the flop. The calling 3 bets on the flop, then waking up with 2 bets on the turn seemed like a flush over 90% of the time. Do people really slowplay 2 pair on a 1-suited flop, then wake up on the turn like this?

In addition, the typical twenty-something player seems much more likely to slowplay a made flush than to check-raise a medium strength hand on the turn.

That being said, I wouldn't have posted the hand if I wasn't worried I had made a mistake here. What to y'all place the probability of a flush being out here as?