Santa is an alien.
He can go to so many houses worldwide in such a short time because his sled is actually a time-travelling FTL spaceship.
That made me remember something from a Christmas Donald Duck story where Donald meets Santa and eventually gets to assist him with delivering presents.
Santa: “Have you wondered how I manage to go around the world in one night?”
Donald: “Yes, that’s gotta be impossible!”
Santa: “No, it’s real easy! Thanks to magical time, a night becomes as long as a year!”