I think any art teacher who outright says "this isn't art" isn't a good art teacher. That being said, as someone who has an art degree and who's been involved in art for over 10 years, my opinion is that art is too subjective to truly define what is art and what is not.
If I had to give a strict definition to what is art, I would say that something is art if it was the creator's intention to be art. At the same time, I could very well disagree with the creator of a debatable piece of art. For example, Hideo Kojima once said that he does not consider his games to be art. I can't remember why he felt this way, but I disagree with him. If we were living in a world where everything has to be black and white, I would say "Yeah, Hideo Kojima's games are not art because he says so," but how I feel is different from what he believes which is why I don't like to place strict definitions on what is art and what is not.
In my opinion, videogames are a form of art. They go through the same creative thought process that everything from a painting to a movie goes through. What's also interesting about this debate is that the definition for what is considered art has changed a lot over time. In the early 20th century, filmmaking was not considered by many to be a form of art. Photography wasn't an accepted art form until the 1920's and 1930's. Some people today have a hard time accepting a video game as an art form, but perhaps in 100 years, it'll be as much of an form as painting or sculpture.
Check out my art blog: http://jon-erich-art.blogspot.com
