Facebook doesn't have access to your email unless you give it access, but I think it is possible to have it fetch friends from your email's address book. Haven't used the feature before, so I have no idea how it works, but maybe you did it when you first set up your profile?
Either way though, Facebook is god damned smart. You might not have mutual friends, but you might have friends who have friends of his, it could have used your hometown or current residence information, education/high school stuff, membership in a facebook group that he's a member of, or any number of other things.