My best friend isn't on Facebook so I don't know how she came up!

If you sign in on Facebook with a webmail like Yahoo mail, Facebook is able to look at your email address book and match it with emails of members... without asking you any authorization ever.
So depending on parameters on your email account (if it adds everyone ever included in a group mail to your address book like Gmail), or what you use, and their agreements with FB, it may suggest very RANDOM people.