The whole discussion on whether or not games are art is pretty limited to the video game community, it's nothing that people who aren't into it think about. To us as gamers, the idea of Pokémon being a work of art, while not necessarily taken for granted, is at least something worth debating, but from everybody else perspective, there isn't really a debate about it, for or against.
Getting a lower grade based on a misunderstanding is sour (it's happened to me too :-/), but I don't think you should get mad at your teacher for not classifying video games as art. If anything, the problem here is that the instructions weren't specific enough, but even then you hold some of the responsibility for not double checking when you knew the subject was in a gray area.
If I were you, I wouldn't call her out for being wrong on her definition of art and ask that she re-evaluates your paper, but rather explain that you misunderstood the instruction and ask to write a new paper on a "proper" work of art instead.