As I suspected, just a random variant from a random never-before-seen universe that happens to reuse an actor for the sake of fanservice. Had absolutely nothing to do with the Fox movies.
No it doesn't. This Xavier had nothing to do with the Fox movies. It could have been literally any actor playing the character, hell it could have been an alligator, and nothing would have changed about the story. The Fox movies were not acknowledged or referenced at all.
It's an entirely different situation from No Way Home, which retroactively weaved the narratives of the Raimi and Webb Spider-man movies into the shared narrative of the MCU. The Raimi Spider-man movies are, at this point in time, the oldest movies to be included in the shared narrative of the MCU's meta-narrative. Xavier in this movie was nothing more than a cute homage.