Even though this was a staged fight, designed to serve as a distraction to the staff, Sam's eyes got very wide at her accusation. They hadn't actually said that yet, though he'd definitely been thinking about it, and it was a little weird to hear it in this context.
He recovered quickly though. "Aw, baby, you know it doesn't mean anything," he said, channeling every douche-y guy he'd ever seen in a bar trying to pick up women. "Don't be like that. I'm going home with you."