Astral Projection has always been a thing in WoW. Or how it was also explained its possible for a spirit to become disconnected from the natural cycle with the Drust. Why wouldn't a "ghost" of Uther be exactly like how a creature in the Emerald Dream can project itself into the world of the living. Especially when the Winter Queen explained the Emerald Dream has the same metaphysical relationship to the living world that the Shadowlands does.
How sad is it for the writers to be like "we're going to let you in on some of the Titan's secrets" and the fans respond "Retcons! Boo!"That's how children always work. You embody the qualities of your parents.