I remember someone saying something about that you can now block anonymous people from that particular post, but they won't be blocked on any other post that person makes. I think it is designed to get someone to shut up on a particular issue, but not block them completely.
Anonymous users can be blocked on specific question as it is written in the FAQ that "If you want to block an Anonymous user on that post only, please click (or tap, for mobile) on "Anonymous" and click "Yes" to Block. They will no longer be able to interact with you on that post, but they will not be blocked on any other post."
I think he/she didn't like your behaviour or points you were making. Forget it.