Nope, it seems like you’re being pretty thorough. I guess Facebook is saying “Hey, looks like these users all logged in from the same IP address. Maybe they know each other, and maybe they know each other’s friends!”. But that would be a foolish thing to do, considering that people login from public computers all the time. Unless they only do it after a certain pattern of use shows up (ie, these X users always login from the same IP address as each other). I’m sure it is VASTLY complicated.
