That is not a new feature, it has been implemented for a while now. It means that either an anonymous QA has blocked an opinion owner or an anonymous opinion owner has blocked the QA. Blocking an anonymous user blocks all comments on that person's opinion. So for example, if I post an opinion to an anonymous QA and I block the QA for that post only, no one would then be able to comment on my opinion. This only happens when one or both of the users are anonymous.