[A_PLUS]

On the flop, I think B3B works pretty often.
I don't think he expects that you would fold a K. But he probably doubts you lead with one too.
This isn't a great spot for him to float with air, since you could lead the turn, and depending on bet sizes, would be getting 2-1 to call a push. I think he is much more likely to try to bluff the flop, if he is bluffing. If he flat calls, I think his range has a lot of hands that beat A high. It is just a guess, but I think we gain more letting him reraise bluff the flop than we do by folding out bad 1p hands.