In this particular case, five people flagged the 'answer' as not an answer. While that's usually an indicator that a post is not an answer, we (moderators) can't take that for granted because users also like to flag incorrect answers, link only answers, and solutions that circumvent the user's problem as not an answer.
So that's part of the problem.
If you flag something as
Not an answer, it really ought to be immediately obvious to people that have no knowledge in that tag that it is not an answer (the other solution, having a moderator for every tag, doesn't scale at all on Stack Overflow).
If an answer looks like it is attempting to address the question, we're going to decline your flag -- and we could be wrong.
If there's any doubt that something might look like an answer to a passerby, then you ought to use a custom flag (Flag -> "Other"), and explain why it isn't an answer.
- This answer is not an answer -- it is meant to be a comment on this answer
- This post doesn't even address the question asked; they may have well posted "Bananas are awesome" for all the relevance this post has
- This was meant to be a comment on the question, not an answer.