I've done art stuff. There's nothing anyone has said that actually proves these being fake. Nothing proves their veracity though either. Other than the fact they would probably go down as the best fakes someone has ever made. Specifically the cinematic shots are pixelated but are still extremely well composed and lighted. That's not trivial visual design knowledge. The talent tree UI is very easy to fake. The dragon race is much harder to fake, but still possible.
People doubted Bolvar and the Shadowlands logo too. We find out soon.