Oh, haha, that's easy! See, not everyone's worlds are exactly the same, so I must just be from a world that doesn't have any Phantom Thieves. I've talked to someone else who's from a version of the world where some of the people are centaurs.

[ the simplest explanation, he figures, and easier to explain than his whole magic time travel business. ]

But that's so interesting! I guess we really lucked out managing to end up with somebody with your skills, huh? We can go looking for clues whenever you want!