He's glad that she's trying to relax, but he also recognizes that it's an imitation of him which is curious. It's like she's never seen this sort of stance or behavior before and is trying to learn it. That sends his overactive imagination on all sorts of benders like martians! What if the little, green men idea is right minus the little and men?

Her comment only reinforces this idea. "Wait--what? I know you did not just say you ship crashed. You putting me on, girl?" His expression is skeptical, but his voice belies a little of the excitement of a little boy who might be learning that aliens are real and moderately friendly (and very hot).

They move into the alley and start toward the diner he's speaking of. She's going to get some stares, but he figures she's got to be used to that then she asks what planet they're on and hooooooly shit. She might actually be an alien. "Earth. Somehow, I think you're gonna tell me that you didn't hit your head when you crashed."