I once got a "Friend" request, and at the bottom were the names of three people "you may know", and I did know two of them, and there's no known connection or link between any of the "befriender" and the two people I knew. The episode scared me away from FB forever. (I clicked on the included "Never darken my doorstep again!" link.)
That was my one and only FB experience, although I'm certain that they've got a record of every public page I've ever looked at, albeit attached to my ISP address, not my name.
Facebook "you may know" is a "six degrees of separation" thing (Millennials or younger, see this
description :/).
Like you said, Facebook can go very deep, so the connection may not be obvious.
