AFAICT, this is a pop psychology book that tries to make some interesting topics digestible to a mass audience. Topics that are mostly speculative to begin with, and don't have concrete evidence in any direction.
For example, the entire field of epigenetics has been argued to be pseudoscience, and yet there has been some interesting research around it. Related to the topic of stress specifically, and how effects have been observed across generations[1].
Clearly, more research is needed, but to dismiss it as quackery outright wouldn't be helpful. Many ideas that were initially perceived as outlandish eventually lead to a better understanding of the world. Scientific progress depends on people willing to go beyond the boundaries of conventional knowledge, often at the expense of their reputation.
This reminds me of the uproar in archeology circles about the work of Graham Hancock. He presents himself as a journalist and author, and certainly not an archeologist or scientist, who simply raises some interesting questions about the past. His work is often dismissed as pseudoscientific quackery, which is funny to me since he never claims it to be scientific at all. It is edutainment content for a mass audience interested in these topics, nothing more than that.