I was reviewing First Posts today and stumbled on this answer as a review audit. To me, it seems like such an answer would be allowed as:
- it isn't spam or offensive,
- it is an answer, as it eventually describes how the answerer solved the problem in the question, and thus it isn't eligible for flagging as "not an answer", and
- it isn't low-quality rubbish that is unsalvageable by editing and thus deserving deletion, so it isn't eligible for flagging as "very low quality".
I think it got chosen by the system as a known-bad review audit because it was downvoted once and then deleted. The downvote seems possible to me as the answer could be wrong, but I think that the post was deleted in response to a flag and moderator error, as this is an answer that does not seem like an answer at first glance, but is actually an answer (if you're willing to thoroughly read it). I've incorrectly flagged such answers before and the flags have been "declined - flags should not be used to indicate technical inaccuracies, or an altogether wrong answer", which I think should have been done to this answer.