As a clinician, I've had these experiences. Clients at Wal-Mart or where ever. If I'm acknowledged, I acknowledge them back. If not, I don't do anything. I don't smile, I don't wave, I don't hold eye contact even.

Sometimes I've seen clients, and they hold eye contact, but I haven't registered from where I know them. It's not intentional. It's just out of context and my brain didn't click "oh that's client X".

I've had clients come to session and say "I saw you at such-and-such place and you didn't acknowledge me!" Oops. I hadn't seen them at all. I didn't even know we were at the same place at the same time.

I wonder if it's that the T "pretended" not to see you. Or if T TRULY didn't see you.