Flat mate a complete stranger - same great grandparent

I'm a white female from California. While in graduate school I moved into a shared flat with roommates I didn't know to save money. Everyone I met before I moved in was an Asian female, and that's who I expected to be living with. Before term started, some of the women moved out and a guy moved in. Now I was living with a 6'4" guy from New Jersey with a unibrow, the non-Asian husband of the only woman I hadn't yet met. (She was still traveling somewhere.) After a week or so I asked "John" who he played chess by mail with (the board was set up in the living room). He said his grandfather - and used the unusual name of my great grandfather. I asked him where his grandfather lived. He cited the town where my great grandfather lived. I asked him what his grandfather did. He was a Methodist minister, just like my great grandfather. His grandfather of course turned out to be the son of my great grandfather, hence we were cousins. I've never even been to this town in South Carolina where my great grandfather lived, but I met another descendent of his, completely at random, in San Francisco, and was sharing a flat with him.