[...hrm. He'd just brush it off, but that might seem suspicious, so maybe he should try to explain it.]

Well, if we were really from the same place, you probably would have. I mean, everyone knows who they are. I'd heard of 'em even before I became Robin. [But something like that wouldn't make him disbelieve her. He was already pretty sure she was legit, so he continues:] So I guess it's definitely alternate dimensions. Same world, but different versions.