I mean in my opinion the principal is the villain being alluded to in the magic route. Like there's someone doing evil magic in the school. Ethan's transformation is likely obviously magic to this person, considering Aurora recognized it as magic immediately. The principal seemingly randomly decides to have beef with Ethan and being out to get them, and while that could be chalked up to "the principal just is that bigoted", I think it would make sense for it to also be motivated by "this person is clearly using magic, I don't want them snooping".