I'd say he's probably drawing, but to what... he could very well have Ad and have hit the board. Or Ad 4x. I don't know how much credit to give BPTK on this board and a laggy player. I'd probably fold his flop raise. Weak, but there's also the possibility of a made straight, a low flush, or anything else on the board that has you beat.

Or he has something out of left field. I didn't expect that.