Facebook "People you may know section"....?

I just recently made a facebook account just to join a tournament ladder at an arcade and i noticed the people you may know section off to the side. What really weirded me out was that they were people that i actually knew, but in my profile all i put was my name and the city i live in, no school or anything else. I havent added any friends either so the friends of the friends thing doesnt apply. Now obviously those are vague descriptions so there is no way facebook could pinpoint who i "may know" down to very specific people. Yet the section shows people i know from my school and people from my school that i used to go to? How do they know?