I'm not the one who flagged this, but "quality check" is perfectly acceptable as a flag reason. Flaggers may enumerate a post's flaws if they choose to, but there has never been a rule requiring this. If a post is good enough, it'll get approved regardless of the flag reason.
The image is borderline enough that I'd hesitate to flag it, but I don't think it should have skipped the moderation queue either. The face seems a little iffy and the hands are just bad. The coloring isn't terrible, but it has the vibe of an artist who's new to digital painting and is still learning effective shading techniques. The whole thing just seems a little amateurish and unpolished overall, and there's nothing particularly interesting about the subject or composition, so I'm surprised that anyone is rushing to defend it.