I don't know anything about his personality or methods of studying music. I'd like to see a list of reasons you think he is an INTP. I'm ready to agree with you.
I'm married to an INTJ with a degree in Classical composition. Through him, I've always understood Classical music to be related to mathematics. (When we talk about composition, we talk about math.) The visual arts can include a heavy amount of mathematics as well. It's lazy of internet randos to assume creative people are Feelers or Sensors. There are many ways to approach the arts.