His stated point is about telling things that everybody is supposed to know.

No, that was absolutely not his point. I don't understand how you could have come away thinking that- literally the entire next paragraph directly stated the exact opposite:

Graduate students in anthropology generally don’t know those facts about average brain volume in different populations. Some of those students stumbled onto claims about such differences and emailed a physical anthropologist I know, asking if those differences really exist. He tells them ‘yep’ – I’m not sure what happens next. Most likely they keep their mouths shut. Ain’t it great, living in a free country?

More generally, that was not a tightly reasoned book/paper about brainsize. That line was a throwaway point in support of a minor example ("For example, average brain size is not the same in all human populations") on a short blog post. Arguments about the number of significant figures presented, when you don't even disagree about the overall example or the conclusion, are about as good an example of bad disagreement as I can imagine.