He shoves there for two reasons. First reason is his opponent is making a very small bet on the turn that basically says "Hey, I have something and wanna play a small pot... So I'm not betting on the river"... By raising your opponent can get sticky with that KQ and make a reasonable call while you have him dead.
Second reason (and the reason I would have led the turn myself) is the two flush draws that are now out there... By calling the small bet, your opponent is realizing his
equity at his price and you want to push away any potential top tier flush draws.
Even though Doug has one FD blocked by his own diamonds, it was not a board you want to slow play on by any means.