As long as your temps and humidity are good (90-92F hot side, ~80F ambient, 50-60% humidity) and nothing has changed in his enclosure, he's probably just being a ball python. Sometimes they just seem to like to sit on top of their hides instead of inside them.

I would also recommend getting another plastic cave type hide for the cool side though, or at least moving the half log so one end of it is up against the side of the enclosure. Half logs are just too open for bps, even with bark stuffed in it. But if these are the same hides that you've had for a while and you've never had any problems, then it's probably not that big of a deal. I wouldn't worry about it unless he stops eating, bps are weird sometimes You'll probably find him back in one of his hides in a couple of days.