The flag declination was absolutely appropriate.

> This was posted as an answer, but it does not attempt to answer the
> question. It should possibly be an edit, a comment, another question,
> or deleted altogether

That is the flag reason you chose, and it's incorrect. The answer *does* attempt to answer the question. It may not be a high-quality answer, but it is an answer.

Flags should not be used to indicate low-quality and/or incorrect answers. That's what the downvote arrow is for.

Seriously, though, it's just a flag. Don't worry about it.