Nope. Not culpable. The ass is just too nice and right there in hand position. Not his fault at all. Whereas that whole almost marking his neck thing? Totally on Balthier.

"So soft on me," David observes. "I'd think you didn't want to leave marks."

And just for that gentleness, he gives Balthier's ass a little squeeze. Nothing to see here. Plenty to feel.