In my opinion, the writer was just trying to write a book and didn't study the process properly from the beginning until they wrote the book and the writer missed a lot so that when he wrote the book it was based on what he knew and was not correct with exact certainty.
What you say is very correct, the author's lack of references means they write based on what they see and don't look for various references that make their writing appropriate to what is happening and I really believe in the four year cycle in Bitcoin and we can see in these few months the price of Bitcoin has experienced good improvement.
Professional writers will look for many sources to strengthen their writing because that is what a writer should do. If it is true that the author of the book did not learn the complete truth about Bitcoin then the book is not worth reading because it will create a misleading understanding for those who read it. That's why not all books are worth reading, and vice versa regarding videos made by people who don't have a clear source of truth.
The conclusion may be that the author is not very professional because he risked his credibility after publishing the book and now almost many people will never want to follow his writing after the facts about the book are quite misleading. Almost everyone knows the fact about four years in Bitcoin and maybe we need to provide education about this to the author of the book.