They did not mention the size compared with primarily Black Africans and Australians with little to no percent Caucasian ancestry in the headline title in the picture of the article you posted
I do not know about the original article which you did not post a link to that I saw
I am lazy
Once I saw this diagram with different head shapes and head stand difficulty for different people
Basically if somewhere at or near the top of your head is more flat it is easy to do a headstand
They make people hold head stands for several minutes for certain Yoga certification levels in certain schools in India
This traces back to India
Now I wonder if this has to do with brain size
Unlikely but funny to think about
@aphron wat about griggers?