This answer, written by who asked the question, is not really an answer, but it should be an edit of the question.
There is a special case in the flag dialog for that:
Not an answer
This was posted as an answer, but it does not answer the question. It should possibly be an edit, a comment, another question, or deleted altogether
Just flag this kind of answers and a moderator can delete them, edit the question or convert them into a comment. But you need to flag these kinds of posts, moderators depend on the community to bring such issues to their attention.
There are also no pro-tem moderators announced yet, although that should happen pretty soon. So the only moderators for now are SE employees that have to divide their attention between multiple sites.
Leaving a comment to educate people is also a possibility.
This is a typical rookie mistake, all you can really do, is try to educate people, or downvote these types of answers. It happens on SO as well.