Facebook Invite - How Does This Work?

I just got a Facebook invite from Jobster's Jason Goldberg in my Gmail, but I get all my Facebook mail on a Yahoo account. I definitely have at least one friend on Facebook who is also an (offline) friend of Jason's, but the invite must not have gone through him because then it would have been in my Yahoo mail. Jason must have gotten my Gmail address from Mattishness or directly from a mutual friend - the problem is that the invite doesn't seem to be tied in to my own Facebook account because of the different email addresses, hmmmmmmm.....