The answer you linked contains barely more than a link, and can be flagged as "Not an answer". There's a really awesome answer to this question over on Meta Stack Overflow.
Quoting a bit from there:
If there's nothing in the answer itself to even hint at which direction we're being pointed in, it's not an answer and should be deleted.
Which is exactly the case, even though the answer has an embedded video. While it's unlikely, this video may later be deleted by the YouTube account that posted it, which would render the answer completely useless.
Answers should be answers, not pointers to where the answer is. Links of this nature should be supplemental, and the actual answer should definitely be in the actual body of the post. This answer should actually explain, in text, how to "break bedrock from above in Minecraft Bedrock Addition".
A caveat to this, though, is... From the same post on Meta SO:
Notice that this is not necessarily the same thing as "link-only answer" (although there is much overlap). In particular, answers where the link itself is the answer to the question are excluded and should not be flagged.
So if a link actually is the answer, it does answer the question. Though, it's best if the answer has supporting text, and isn't simply a link with zero explanation. Context matters!
As far as flagging as spam goes... The Stack Exchange network has a pretty clear definition for what they consider spam. From the FAQ on spam:
A post should be marked as spam only if it advertises a product, service, or similar and is unsolicited or lacks disclosure.
If the answer you linked had simply been promoting their own YouTube channel, it would be considered spam. I don't see any connection between this channel's author and the answer poster, so there's no undisclosed affiliation there, and it doesn't really appear to be promoting this channel. The lack of these critical requirements makes it NOT spam. The answer was trying to answer the question, it was just doing it in a way that Stack Exchange's quality guidelines recommend deletion for.
In addition, spam flags (and Rude or Abusive flags) are special. Once a post reaches 6 of them, it is automatically deleted and locked by the system, and can't be undeleted by users with access to undelete votes on answers; it requires a moderator's intervention. They also carry an implicit downvote by the system when a user casts one on a post. You should make sure to use them with care!
Lastly, you said:
If I review stuff and don't report it, I get my reviewing privileges taken, so I have to report it somehow or I get review banned. But if I report stuff wrong, I'll get my reporting privileges suspended.
If you're not sure what action to take in a review item, there is ZERO harm in using Skip! Reviewing is a very helpful, but optional, moderation process available to you. If you're not 100% sure in the action you're going to choose, skip it, and spend your flags on stuff that you're absolutely sure need them.