He's someone who has been here before, Xiao Xingchen, but now he is from later in his timeline, after he was blinded, it seems. Actually, he is from after his own death, so he's a little skittish right now.

Ah. I...guess I thought someone would have told you. Your other self, Prompto, and Gladio have all left the Train today. [He also lists the others who left, because he wasn't sure who all Noctis was close to.]