I declined the flag, for the reason stated in the feedback itself.
Although it was little more than a link, that was indeed an answer, it was coherent with the topic of the question and - through the link - it was providing with good content.
If you don't like it, you have other ways to act before thinking to flag it:
Edit it, adding the content that you think might complete it (in this case, a summary of what the video explains). This is a very valuable contribution that you give to the answerer and the site in general, and it also gains you some rep.
Comment to the answer, saying that it should be something more than just the link, and asking to add the content, as descripted in 1.
Downvote: if the answerer doesn't act over your feedback, or if you think that it may misguide the readers, or if you think it's low quality in general - that's your way of informing the community and the user itself of your opinion.
NB: I didn't mean to reject your contribute, which is always welcom and often useful, just pointing out that flags should be used when you don't have other ways to fix.