"Figure Figure11 shows a mountain gorilla lying on the ground on his side without a pillow" - Of course it is without a pillow, it's a mountain gorilla! What is this clarification?
"To start with, some Westerners have to hold on to a doorframe." - Would it not be better to say "you may have to hold on" or "newbies"? It is not like Westerners have some special physiological feature that makes them do it, it's about lack of practice.
Nevertheless, after reading the article I have seen that the clarification about the gorilla sleeping without a pillow made perfect sense in its context, because it has not been added to provide any additional information, but it was added for emphasis, in a context where the sleeping positions in modern environments were contrasted with their correspondents that are common both in non-modernized environments and for similar primates.
Moreover, I interpret his phrase "To start with" as having the same meaning as your suggestion "newbies".
Using a door frame in the beginning is indeed good practical advice for achieving the full squat position for those who are not used to it.
So, gorila sleeping position implies exactly nothing for my sleeping position.
Tribes people don't live instinctually. They have culture, like us. The critique here is our culture could benefit from observing how their culture does it.
You can look at the COVID pandemic for an example of how body positioning has helped change how well people can breathe. Proning of severely sick patients substantially improved outcomes. That's literally just rolling the patient from their back to their stomach. So there might be something interesting there that we can learn if we pay attention. And he's trying to say "we can learn something from these people if only we pay attention."
That doesn't follow at all. Gorillas are well known for their habit of making nests. Making pillows isn't difficult.
(I don't use any of these positions, but I most commonly nap on a heated wooden floor in an insect-free environment. Oddly enough, I also support my temple on the dorsal surface of a wrist; it had never occurred to me that in addition to comfort, it keeps both ears free?)
Lack of practice causes a "special physiological feature": ankle inflexibility. For some people it would take a significant amount of time stretching the ankles every day to recover enough ankle flexibility to squat, and that could perhaps still be insufficient, as joint mobility is established based on the range of motion used in childhood.
So at which point/age do some of us stop doing that type of squat before "use it or lose it" kicks in?
Funny old world.