This article is a bit unclear in that it seemingly refers to the WCAG 2.0 guidelines as rules. In the aXe tool, each criterion is referred to as a rule for the sake of writing tests, and only the guidelines that would present zero false positives when tested against, (excluding, for example, the alt attribute, since if it exists, any automated tool will flag it as good, while determining whether or not that is actually true depends on how the alt attribute is written). It needs to be kept in mind that, while you can automate accessibility checking to a point, any automated tool, including this one, is only going to get you about 30% of the way there. These tools aren't designed to be the final say on accessibility as a whole, but to act as a sanity checker. This is because most accessibility errors end up being repetitive across a site or CMS. It's also helpful to keep in mind that the WCAG 2.0 are guidelines designed to help you implement the HTML spec.