My opinion is that yes, graphics code reviews belong to Computer Graphics.
While Stack Overflow is a very large community and it makes sense to consider Code Review to require its own dedicated website, I think the same isn't true for a narrow field like Computer Graphics. Based on the low activity, it wouldn't make a lot of sense to divide it even further.
On the opposite, Code Review probably wouldn't be the best place to as for graphics programming related code review, since insightful comments require some expertise, or at least experience, in graphics programming.
Moreover, I think this is typically the kind of discussion where people with experience in the field (AAA game, etc.) can contribute greatly, beyond answers that could be found in papers.
We probably want to put a limit to the breadth of asked reviews, but I suppose common sense will tell when to use the "Question is too broad" flag.