Hi and thanks for the post.
Not an answer flags are the most misused flags here by far.
Duplicate answer indicates that the post is an answer. You should choose an other flag in this case and explain the issue.
- wrong answer, don’t flag as NAA
- bad answer, don’t flag as NAA
- answer needs an edit, first make the edit (or wait for someone else to edit) then flag appropriately.
The main post here covering declined NAA flags is Why was my flag for "not an answer" declined?
TL;DR - moderators generally don't delete posts until they have several down votes or constructive comments if there's even a hint of an answer contained in the post
So I declined your flag since there wasn’t a single effort to help the op. No comment, no vote, no edit. The person was clearly trying to answer, so I chose to leave it up.
When you detect a pattern of bad answer, absolutely flag them as other, but the harm in having basically duplicate answers with different wording is actually a benefit. Search engines index all the words and when people use different terms for the same thing, that makes the pose easier to find. Deleting content can harm the site overall. That is why when we close questions we like to keep 10 or so duplicates around before we try to start merging them or deleting the least useful versions.
Same for answers, rather than flag a bad answer, spread some upvote on the better answer and possibly the question.
Putting attention into the best answer rather than worry about culling less good ones that will end up below the fold would be my “advanced flagging” advice.