Hello, John

This July, I visited Cambridge, MA for a conference at the MIT Media Lab. There was an experience there that has stayed with me, since visiting. I came across the location of this event in Google Maps, which you see above. I visited the establishment known as the Flour Bakery and Café each day as I walked from our hotel to MIT. I had several delicious iced coffees there. The first morning there, probably at around 7:50 AM, I was waiting for my colleague to receive her pastry while I stood near the door with my aforementioned iced coffee. Another customer was coming near the door; he was a man, older than me, with some gray hair, I believe. He also had gray facial hair. I believe he was wearing glasses. And he was dressed professionally. What shocked me was that he said hello to me. Using my name. "Hi John," and he smiled. He walked past me, and out the door. I first thought I must be wearing a name tag from the conference. Nope. We hadn't gotten name tags yet. I was wearing no identifiable labels of any kind to identify myself. So, since I really didn't recognize him, I can only imagine one of several possible scenarios: 1. He does in fact know me "in person" and I did not recognize him. He must have an excellent memory. 2. He recognizes me from the Web. 3. He recognized someone he thought knew, who also goes by "John." What's odd is that he didn't stop to chat or tell me how he might have known me. This is a mystery I want to solve. I don't know where to turn next. What does anyone suggest?