The author is missing one law of design that should be explicitly stated here: different things should look different and things that look different should be different. The example under "Don’t dance all over the color wheel" is a great example of a violation of this rule: it goes from showing five different things in bars to showing two groups of two plus one different thing (or a group of two and a group of three, it's actually not very clear). One of those interpretations is wrong, or unuseful, and careful color choice can make the right inference the correct inference.

This mistake is repeated in several places. But there's an example of where it's done well just below the heading "Avoid bright, saturated colors", where the colors suggest a relationship that in fact does exist and is meaningful (Asia is in blue).

And note that this isn't about banning similar colors from use. It's about what goes wrong when they're used in proximity, and exclusively so. (By chance a couple times in a big graphic is fine, since there are many places they won't be together, so no real implied relationship exists.) Of course using similar colors exclusively distant from each other is a straight-up confusion risk, so it's still an issue.