You have to realize that MOST books are penned by freelance writers not engineers or even engine builders. They simply write what they have read from other sources or what they have been told.
I have a friend who has been making his living writing "how to" and research books without any knowledge of the subject. He simply repeats what he has been told. 50 years as a respected author of automotive books. Former editor of one of America's largest weekly automotive newspapers. And he can barely change his own oil!
So consider the source of all information.