there are a thousand different reasons for not wanting to deal with reality. . . .The sad thing in this situation is that the person is a therapist and perhaps he is "pretending" not to see you. If that is the case, his decision to not acknowledge you is unprofessional and sadly immature. As the professional, it is his job/mission to be the one who steps out of his comfort zone and be the one to be brave and authentic. I can only hope that he didn't recognize you.

There is a small. . .and I mean miniscule chance that the individual didn't recognize you, but that seems pretty slim. I mean, he came into the room and walked directly toward you to address the person sitting next to you (if I'm understanding the situation correctly). I know that I have severe difficulty recognizing "acquaintances" in strange or different situations. Sometimes people thing I'm being rude or disrespectful and it is about facial recognition. That might be your former therapist's problem. I don't know. You'll only know if you gently talk to him about what happened.