There are a number of issues being discussed here, though related they are quite different.
The issue of plagiarism on the layout of a book by cherry picking or accessing a couple pages is ludicrous. there are only so many ways to layout graphics and in any visual book you can find similarities. Until the entire book can be compared there is no way to say if the look and layout was copied.
As for the topic/steps/mechanics of inking, these terms, demo's/examples and tools have been universal for many lifetimes. My instructors in college were world level artists and far removed from jake. They used the same examples shown in the pages shown. It's ridiculous to think one person owns any method that has been used for generations.
The gentleman on youtube has acted out like too many on social media and online, react and attack. what happened to thought and discussion? I can't say legally who is right as I am not an attorney or expert but using common sense clarifies it in my mind.
As for sites cancelling "inktober", don't come down on them without knowing their reasons. They could just be tools who are reactionary or they may simply want to avoid any issues with using a trademarked word. trademark is far different than copyrights. A trademark owner is required to defend their trademark or risk losing it and/or having it enter public domain. While a trademark owner may be willing to accept loose enforcement and let the mark be used - attorneys and publishers are not so willing to be nice. When Inktober was trademarked the owner I am sure realized, or should have realized, not only would there be flack over registering what what others were encouraged to use but that there would be damage to that brand that would affect participation. the phrase went from being a community activity to an activity that was owned (in name only but owner nonetheless). I'm not so sure the trademark would have been granted had opposition been submitted during the filing period with clear examples of the history of the phrase.
It is disheartening to see artists, who are supposed to open and willing to explore openly attack Jake the way they are. I guess I wrongly believed that creative people were the type to not jump to conclusions.