Phantom Baldi appearing in random mode probably doesn’t have any meaning to it and it’s because the map that had Phantom Baldi was actually part of my level called "Baldi’s Tragedy School" which doesn’t really have any some sort of lore to it and is more like a map made for fun. It’ll make sense in adventure mode when future updates arrive.
Also, Baldi sprite had already been changed since development of beta 1 which uses saintza4 Baldi model.