Why am I getting "do you know this person" from Facebook?

Today I was looking at my friend’s friends and noticed someone whom I do know and would undoubtedly be happy to hear from me.

I get a message, “Do you know X personally?” It threatens to block my request as spam if I don’t. OK, how does FB know that?

I hit the button that I know the person, and it blocks it anyway. I have no idea why this message comes up with certain people (I’ve only seen it twice now). Can someone here clue me into the logic of how this works?

Thanks!

Surely someone can help?

How many other friends in common do you have with this person, other than the one through whom you found him or her?

possibly there is a filter on the other persons end that blocks friend requests from people they dont know.

How do you know that it was blocked after you said that you knew them?

A notice came up to that effect. This is on hold, or something.

Maybe it said it was pending their acceptance. Which is standard on friending anyone on Facebook.

Yeah, after you friend someone, you get a message saying that they need to accept the friend request, and it’ll be ‘pending’. Is that what it was?

No, it was something else. I should have noted it down. I guess you guys haven’t seen this before?

I get a similar message once in awhile. My theory is it’s because I had a conversation with that person through a mutual friend’s page. I get that message even though I personally don’t know the person. The Facebook robot is being too efficient.