A while ago, I flagged an answer as "not an answer", because I believed that it was not actually addressing what I believed to be the OP's main concern (i.e. the difference between the various words for "today"). The response I finally got more than two weeks after the flag submission was:
declined - flags should not be used to indicate technical inaccuracies, or an altogether wrong answer
This appears to be a misunderstanding of why I flagged in the first place, but that's a bit beside the point. Similarly, when I flagged a different answer for the same reasons, I received a response of:
declined - a moderator reviewed your flag, but found no evidence to support it
This reads more like an automatic message, but that's a bit beside the point. (This flag I submitted because it only gave a general explanation that didn't fully address the problems presented in the question.)
If these flags were rejected, then when am I actually supposed to use "not an answer"? Clearly answers that are actually meant to be updates to the question should be rejected, as well as responses to others' posts. Similarly, answers that are downright wrong or that don't do anything beyond "This is wrong, and you must have misread the text you are quoting in the question." should simply be downvoted, since technically speaking they do give an answer.
But this doesn't deal with the issue of answers that don't really engage with the problems of the question (and in this sense, are slightly different from partial answers). Nor does this strike me as simply "missing a detail" in the answer, where more lenient flagging might be justified (see here) -- in the second case, nothing related to the OP's question seems resolved (although a gloss is provided, which could be useful).
Is "not an answer" also meant to be used in such cases? If not, this would seem to differ from the practice I've seen on other sites (e.g. where link-only type answers tend to be removed, or where answers tend to be removed if the detail they contain is so limited that they fail to really resolve any issues).