Has facebook ever logged a friend of yours in even though they've never logged in from that device?

[Edward]

I went to log into soundcloud from my girlfriend's ipad. I used the "log in using facebook" feature expecting a log in screen. Instead it logged a friend of mine in, meaning he was signed into facebook. I asked my girlfriend about it and she said she hasn't seen him in years. I want to believe her but this sounds absolutely outrageous to me. The only answer I can come up with is that she's lying. I've searched the internet and not one page showed up resembling a similar problem. Someone please ease my mind...

[Jon]

Can't help you ease your mind. Facebook doesn't log random users accounts in on other peoples devices. Even if they did, what would seriously be the odds that random someone would be someone you knew.