I would not address any of them that I was seeing as dr. Or any other title unless they were addressing me formally too. I stop mds who try to use my first name if I don't know theirs.
I don't call the therapist anything in person. There are only two people in the office and I am clear on who is who. The therapist in the OP at least does not assume familiarity while expecting formal address towards them. If it bothered me enough, I would find another.