In general, when flagging, you have to realize that the moderator who deals with the flag may not be familiar with the technologies that are referenced in the question, so what might look like a non-answer to an expert, might look like a bad answer (or at least a reasonable attempt at one) to someone else. As a guideline, if an answer even appears as if it is trying to answer the question, then a flag would likely be declined.
For this specific question, there are 2 things that should have jumped out at you before flagging.
- The answer is ~3 years old
- The answer has had 4 downvotes since 2010 (the 5th was picked up this year)
When you have a heavily downvoted, old answer (or non-answer), the chances are it has been flagged many times before, so the likelihood of declined flags increases.
I'm not saying you should haven't have flagged it because old garbage is missed all the time, but when you run into an old post and decide to cast a flag, you have to be prepared for it to be declined. When you in into a similar post, if you truly feel like it is absolutely not an answer, a custom flag explaining why might be a better choice than flagging as "not an answer". This way you can explain why you think it is not an answer so the moderator who handles your flag understands your motivations.
Alternatively (as suggested by @jmort), you could have left a comment explaining why you did not think it was an answer and how it could be improved, and then flagged with a regular
Not An Answer flag. In doing this way, you allow a 10K or 20K user to handle the flag instead of a moderator (if for no reason than to ease the burden on the moderators).