It’s a clever feature and it’s handy that there’s an indication of what happened. But that notice counts as a reply! I think it’s a bug because it’s a notice that’s stored in a post rather than a real reply. I’ve been looking at maybe submitting a PR to Discourse to fix that.
By the way, that problem also shows up when you look at the category listing:
But it’s way more obvious when you look at the bottom of the post and can count how many actual replies there are compared to the number.