A good way of answering this question, since so many people seem to be confused, is to draw a parallel between a gifted studio musician and a piano player who only knows one tune.
Psychologists have varied proficiencies to draw upon when treating a patient.
Besides varying clinical perspectives, there is biofeedback, relaxation strategies, EDMR, assessment tools, and the like. When a psychiatrist does interact with a patient in a more traditional manner, the emphasis typically is Freudian psychodynamic, which was most probably learned in a neighborhood institute for psychoanalytic studies. Psychologists, on the other hand, prefer to obtain clinical skills in a university setting. Now all of this might seem self serving. Perhaps it is.