I think they just err on the side of false positives. You can always ignore the friend suggestion if it's someone you don't know. If they fail to suggest someon

I think they just err on the side of false positives. You can always ignore the friend suggestion if it's someone you don't know. If they fail to suggest someone you do know, that's a missed opportunity. Some of this is inevitable. For example, their algorithm was eager to suggest one particular person to me, and it did so multiple times even though I did not know the guy. It was someone who had worked at the same company as I did, in the same department, but quit the company slightly before I was hired. So he and I had easily 10 Facebook friends in common. Facebook had good reasons to suspect that I knew the guy. Even though I didn't, I might have, and they have no way of knowing for sure, so they might as well just ask.