Firstly, I would recommend posting this at r/anthropology. Secondly, no the author is wrong on a few counts, generalizing a large and diverse numbers of people is just one if the flaws. The author's first red flag is describing the naturally pure "garden of Eden" state the new world is in. This is not supported at all by archaeological evidence and North America was highly developed in different areas. I recommend 1491 as Charles Mann as an introductory text on this. Next I will attempt to describe what I know about the Navajo two spirits. Gender was a spectrum. But the individual did not decide where they were. The family stated the person's gender. This could be used as a social force to say, get an older woman to marry due to ostracized traditional roles. Also, some two spirits were important in ceremonial roles. Visions and ritual were their domain. However, a bad harvest after a ritual for a good one could often result in the execution for the two spirit. TL:DR the author over generalizes and tries to place a pretty noble savage picture. Where the known history is far more complex and bloody.

(Typing this on my phone sorry for any errors).