Art is the subjective component of human creation.
Is it subjective? Is it created from humans? Then it is art.
Videogames are definitely art, and one of the richest forms of art by the way.
Most of people have other definitions of art, which are not as solid and incisive and this one and some are even by enumeration. For example, some people say "art is books, paiting, sculpture, music and movies". I call this the private club of the person who said such thing.
Definitions can't be made by enumeration. This only happens when people don't have any idea about the concept they are trying to define.
Some of these people, and I presume it's the case of that teacher, are too conservative when thinking about art. Only things with centuries or millenniums of existance can be considered art (in their minds). So I guess they would reject movies when they first came, claiming that only theatre was art. And that they would reject books when they were invented, claiming that only painting was art. Now it's the time of videogames to be rejected.
There is also other mindset that is based on quality. Only quality things can be considered art. This logic + ignorance about videogames lead a lot of people to claim that videogames, that weird thing that addicts our youth and makes our childreen to become violent, that can't be art. I won't even tell about how ignorant they are, just that they are incoherent because if music is art and there are a lot of music tracks that are superficial and lack of quality, then they couldn't be considered art. But they are.
Art has nothing to do with quality. There is good art and bad art and that is even subjective.
Prediction made in 14/01/2014 for 31/12/2020: PS4: 100M XOne: 70M WiiU: 25M
Prediction made in 01/04/2016 for 31/12/2020: PS4: 100M XOne: 50M WiiU: 18M
Prediction made in 15/04/2017 for 31/12/2020: PS4: 90M XOne: 40M WiiU: 15M Switch: 20M
Prediction made in 24/03/2018 for 31/12/2020: PS4: 110M XOne: 50M WiiU: 14M Switch: 65M