Even if all the Meta downvoters come against this, I'll say that it was a mistake of moderator to decline your flag.
In less blatant cases, I prefer to advise on safer ways to flag stuff like that or whine about slippery flag description for not-an-answer. But when I looked at the answer you flagged, I thought WTF, this is slippery? give me a break!
The answer you flagged is link only, pure and simple, it does not even pretend to be anything else:
There is a pretty strong community consensus that "links... should never be the only piece of information in your answer".
How to Answer instructions even have a dedicated section Provide context for links requiring: "...Always quote the most relevant part of an important link..."
That is, the answer you flagged has serious problems and no matter what flag you used, there is a clear guidance in SE Moderator Newsletter to dismiss flags in cases like that as helpful:
...Users are asked to flag posts to help keep the city street clean. Even if you feel the flag was not technically correct, you don’t want to continually send the message that their help is no longer wanted. That is not what the feature is about.
We clarified the guidance for when to dismiss a flags as
dismiss flag on this post as…
[helpful] the flags have merit but no further action is required
[declined] the flags are unhelpful or noise
Given the evident problems with quality of the flagged answer, your flag is neither unhelpful nor noise.
It is perfectly reasonable to expect of moderator to be able to recognise that and act per Mod Newsletter guidance. The fact that this did not happen is a mistake of the moderator who declined your flag.