Ash wouldn't exactly try to trace it to Carmen or anyone in particular, so to speak; since the people here come from so many worlds and the thief's identity would not endanger his family even if they showed up it wouldn't be his priority. The part that would truly interest him is a)whether that person still present in Johto and b)what else was there beyond that sweet, sweet chair*. Which is the kind of info that could (not so) easily be obtained from an anonymous person on the network or from the very male and dashing El Zorua if needed.

Besides, he knows damn well the advantages of anonymity and fake identities. This is a guy who didn't tell his family he was alive for thirteen years so they wouldn't get in trouble. He even got an haircut and a new paint job for his giant robot! So no rude prying about other people's names and stories, thank you. He'll be polite and businesslike and rather admiring, because wow pulling that off without the resources thieves generally have in their own worlds.

*His own is still totally better, though.