In general, the ♦-moderators do not moderate the mathematical content of the site. We're not here to ensure users employ the correct mathematical definitions, notations, or conventions. We're not even here to ensure that the answers provided are correct.
Regarding the specific flag you mention raised on this answer: it was declined, by myself, on Jan 23rd, less than 90 minutes after you raised it. I declined it with the following comment (which you should be able to access by clicking on the number(s) next to the "helpful flags" item in your user profile):
This should have been a comment to the post.
In general, when you see things that are possibly mathematically incorrect (or using the wrong definition, convention, etc.), you should comment on the respective post pointing this out (or requesting clarification, or whatever). This will allow you to engage with that other user, and find out what the source of the disagreement is (and maybe everyone learns something!). I am personally at a loss about what you even expected the ♦-moderators to do in this case.