Jack had a thought that he'd be invited to stay when John said he should sleep and then said he should come in. And the door being locked with Jack on the inside basically confirmed it. So he's not surprised by the suggestion, exactly. He does give John a considering look of his own, because no, he's not seeing any signs that this is an attempt at seduction, even an inept and slightly threatening one. Jack has been on either side of a fair number of seduction attempts in his time. He knows what they look like.

So this is... a friendly bed offering. Which Jack is also not unfamiliar with.

"You are okay with that?" is what he asks first, expression sober. "After we... fought last night? I am pretty sure we fought last night."