The deletion reason field is just a textbox. We can put whatever we want in it.

Considering that humanoids, even things like elves, are still considered relevant enough because they have nonhuman features, there isn't much of a reason to have people say "it's too close to a human". The human-only posts get deleted because there are no discernible nonhuman traits, otherwise traits that would make them nonhuman.

Edit: Skin color isn't used as a factor because human skin can already vary wildly in color, whether it's natural or artificial. Tattoos/dyes and things like argyria exist in the real world and don't make something less human.