> I understand from this that the poster has prepared both in advance
> and posted them both simultaneously, maybe as a way of getting
> upvotes.

When you submit a question, you are given a chance, to also answer the question.  Both the question and answer are submitted at the same time when you do that.  [I have done it in the past myself](https://superuser.com/questions/1009309/windows-10-v1511-mounting-external-encrypted-drive-error-the-parameter-is-inc), when I had a problem, and already knew what the solution to that problem was.

I doubt it has anything to do with earning reputation.  The user had a problem, knew the answer to the problem because they figured it out, and thought other people might have the problem.  **We should encourage this behavior.**

> I'm wondering if there is something wrong with what this poster did,
> publishing an already-solved problem. And if there is, what we can do
> about it.

Users are encouraged to self-answer their question.

[![enter image description here][1]][1]

 
> As SU is a Q&A site and not a blog, this case seems to me to be in a
> bit of a gray area. We are all supposed to share our knowledge,
> Q&A-style. But this method, if it becomes common, can mask questions
> by users that have legitimate problems that need solving.

  **I don't see how the question nor the answer, in this case, could be considered a blog.**



  [1]: https://i.sstatic.net/jjWsF.png