MD vs PT. A physiatrist is a medical doctor/physician who specializes in rehab medicine. The physiatrist went to 4 years of medical school followed by an additional 4 years of specialized training in physical medicine and rehabilitation. A physiotherapist, also known as a physical therapist, is not a medical doctor. They may have a phd, thus are "doctors", but they are not ever physicians.
Training. A physiatrist is a medical doctor who diagnoses or treats musculoskeletal conditions. They can prescribe medications or physical therapy for treatment. A physiotherapist or a physical therapist is trained in anatomy and kinesiology and can provide patients with therapeutic exercises to improve their conditions.