Answer:
Both a music teacher and a music therapist teach music. The difference is in why or how they teach. a music teacher teaches someone how to play an instrument for a performance or a band or for the sake of learning how. a music therapist teaches someone how to play an instrument or shows them different songs or types of music for therapeutic reasons. this could be because of a medical diagnosis, stress, depression, anger or anything else you can imagine to help them feel better or work through whatever they need to work through.
at least that's what I think. I'm not entirely sure but I hope that helps!