Appears on old questions that were marked as duplicates before the new closing overhaul. These notices were edited directly into the question by the Community user and could be freely edited and even removed. This has since been replaced, but questions that previously had it were not updated.
This question already has an answer here:
The new default message that is shown to everyone when a question gets closed as a duplicate. It is an automatic box that is displayed and can only be edited by gold tag badge holders or moderators via a special edit link at the right.
This question may already have an answer here:
That solved my problem! No, my question is different. I will edit to explain how.
This message is shown to the author of the question only when it has a pending close-as-duplicate vote or flag on it, until the question either gets closed or the duplicate vote or flag expires.
This question is an exact duplicate of:
Looks like this is a special case for when you close as a duplicate of another question that doesn't have any upvoted answers.
On normal sites, normal users can only vote to close as a duplicate if the other question has an upvoted or accepted answer (moderators can bypass this). On meta sites, however, any question can be closed as a duplicate of another question, no matter if it has answers or not. So naturally you'll see this possibility a lot more on a meta site than on a main site.