Reading through the article, I very much sympathized with the author's Dutch attitudes towards American mannerisms. And I'm American.
All of my life I've felt at a distance from others who exhibit typical American social habits, and have actually got along better with people from various other cultures such as eastern Europe. (There are a lot of first and second generation immigrants from eastern Europe where I live in the US.)
I have always been perceived as rude and blunt, and in recent years those with typically American social attitudes have even begun pathologizing behaviors like mine as being "on the spectrum".
As to why I am like this was a mystery to me in childhood. I acted just like my family and extended did! Everything was normal at home, and then I would treat someone at school like I would treat a sibling and it would result in arched eyebrows.
Turns out my family's attitudes towards socializing were strongly influenced by my mother, since she was a stay at home parent. And she came from a part of the US made up of small agricultural communities that were mostly German and Dutch in origin. These small communities had transplanted their national cultures in little bubbles all over the US, and by dint of mostly isolation from the broader culture had maintained those mores for centuries.
It was only when my mother had moved away to the city that this culture shock occurred, about 150 years after immigration.
So yes, there is a lot of cultural variation in the US, probably not as much as in Europe, but it exists. There are subcultures within the US of various vintages that exist alongside the mainstream culture that have all learned how to be different and coexist at the same time.