"How do you know me? We've never met..."

I was on a trip with my cousin in Colombia and we were living very cheaply and moving without a plan, just following the tides. We ended up in a tiny town in the north of the country and the only industry there was scuba diving. So we decided, let's try scuba diving. There were about 15 different scuba shops in the town and we had no idea of how to choose one. We just walked down a side street and went into the first one that looked appealing. We asked them if they had any English instructors, they said “Yep we have one. We’ll book you with him tomorrow." We show up the next day and our instructor comes over to greet us and I say “You’re Federico!” “Yes, but how do you know who I am? I’ve never seen you before.” “I’ve stayed in your house. I've actually slept in your childhood bed. I recognized you from the photos your mom showed me.” “How did you end up in my house?” “Remember Tommy, the exchange student who your family hosted three years ago? He was my college boyfriend, and I visited him in Buenos Aires and your mom invited me to stay at your house. You were away, but I heard all about his host brother Fede.” I am American. He is Argentinian and we found ourselves paired in a tiny town in northern Colombia. A random town, a random scuba shop, a random instructor that I knew but I’d never met.