Charlie's immediate, bone-deep response to being asked that sort of question is to lie, so his demeanour is immediately casual again. If you were dropped into the scene from space with no prior context, it would be convincing.

(We know, we know, and it's exhausting for him too.)

"Nothin', just, uh- you two never mentioned we had a missed connection." And he's glancing at both of them here. "Surprised me."