I think his point is that using bright color for "empty" part of the circle and "light" color for the filled one is counter-intuitive on dark background because it's "backward" to what you'd expect.I think you should look twice at the image because you are missing something.
It works "as intended" when the background is bright/white:
but then a supposed perfectionist should at the very least check what it looks like in dark mode, and realize that making the background transparent in that .png isn't a good idea.