I got a friend request from a friend and classmate who passed away in 2015 the other day. I knew it was bogus and played along and got the same bs you did. Before I could call him on it, the messages disappeared and were replaced by something from FB about the messages being deleted. Just when I was having fun! Yeah, it's apparently not too difficult to hack a facebook account. Beware when receiving a friend request from someone you're already friends with.