Is it appropriate for someone in the therapist's life - be it a partner, family member, or friend - to sit in the clinic waiting room waiting for the therapist to finish her day?

I was the last patient of the day. I left the clinic room through the back door, but went back to the clinic less than a minute later to ask the therapist a quick question. When I entered the main front door of the clinic, I saw someone sitting in the waiting room. We made eye contact. No one else was working at the clinic at that hour; it couldn't have been a patient. My intuition told me it must be someone in the therapist's personal life. I didn't recognize that person as someone who worked in the clinic either. So true enough, I saw the therapist and this person together hand-in-hand walking outside the building.

I know that I should talk about my feelings and reactions with the therapist. But is it appropriate in the first place for therapists to bring someone in their personal life into the clinic waiting room? The therapist's personal life should be kept private away from patients unless it is beneficial to the patient. So why bring someone in your private life into a professional setting? Even though the waiting room is a public space, it is still part of the clinic. Any thoughts?