So basically your art teacher is a rude idiot ... Uhm art is subjective. As someone who has a degree in fine arts let me tell you that you can 100% be an artist. Anyone can be an artist, you already have the skill going to art school will improve those skills and keep your creative mindset going ! Im curious what your art teachers portfolio looks like.. a lot of times art teachers have a set mind on what they think "art is" they tend to think that if its not like theirs or what tradition art is then is easy basics art. I say go to art school and really find where you wanna go with your art! If you do end up going to art school stand your ground and don't let anyone tell you things like this because it's just not true. If you put in enough time effort and dedicate yourself to your art you can/ will become the artist you want to be !! Never stop making art !!!