Isn't most of the text on the page grey? It's not white, it's rgb(215,215,216). And the background is not black. Some worse examples are shown, but then the message comes across as "don't use grey unless you know what you're doing, like I do, because I'm using grey while I tell you not to use grey, but mine is okay."

Maybe aside from the unset option, something more specific about a minimum contrast threshold would be useful. Ideally the author wouldn't be breaking below that threshold themselves while explaining it.