TL;DR: This document is for creating a themed FANTASY setting, not for teaching real world HISTORY.
You're missing the point. This is not meant to be an accurate description of world history. This is for creative minds who might not know where to start when it comes to feudal Japan, ninja, samurai, etc. who might be interested in creating a fictional fantasy world setting for playing tabletop games, journaling, adding flavor to existing medieval adventures, etc. If someone has the itch to go and read real history, that's a bonus in my eyes.
In my writing project, my world of Old Nippon has dimensional portals and people from multiple eras and worlds being thrown into the setting, with local people trying to take advantage of them. For my purposes, the information I've gathered is fantastic, as it allows me to skim through a page or two for obscure details I don't have time to research, and this gets me back into the story right away where I can keep the plot moving. Four dollars is a fair price, I think, for a 250 page book on a fictional setting based on / inspired by a real world era.
I have seen for myself that AI is not providing true results, so no, I wouldn't try to teach a class with this information. Having said that, I looked for a ttrpg setting based on feudal Japan, and could not find one that suited my needs, so I created my own. You may have missed this part, because you don't mention it, but HALF of this book contains FICTIONAL characters, locations and adventure scenarios.
Having said that, I appreciate that you've taken the time to go through the book. If you'd like to have a conversation on this topic, see my bio page for a link to my writer's blog, and I will add a reddit link to that soon. Thanks for the comment, and for the concern that, when it comes to presenting real history, I agree that people should get their facts right.