The capitalisation of photorealist is incorrect. There's nothing unique about the word or the artist.
Student or Learner
Why is this "Photorealist" capitalized? Is it because it's unique?
12)Chuck Close is a famous American artist 1)known for his portrait paintings. More than just a painter, photographer and print artist, he is a builder 1)who, in his words, builds "painting experiences for the viewer". He first achieved fame 1)as a Photorealist in the 1960s.
I agree with you that it's possible to say "He was a photorealist" simply as a description of the kind of photography he took but if he was one of a recognised group of photographers called "The Photorealists" (and given that it says that he found fame that way), then I would say the capitalisation was correct.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.