I lead out on the flop, ~$1.75, due to the fact there's two to a flush and I'm always very stabby at paired boards in heads-up pots whether I have 2p/trips/air

Given his stats, and assuming a decent sample, his line is weird. rest of the hand is ok, you can valuetown most people here because Ax is a good part of his range, and 5x isn't, and you know the highest flush that can be drawn to is with Qc