@pixel-dsp I guess it really depends on what the content is and how it was approached. But let's go over them:
Terms: In this case, the actual content is very basic common terms and shapes that all teachers use. They are so basic and common that there is literally no other name for them or way to phrase it differently. To talk about Line, form, shadow, detail, etc. is common to all drawing. If I did a drawing class, I would use the same terms (and have used the same terms). You just can't have a drawing or painting class without using those exact terms. They are the building blocks of art.
Sequence: Just like the "Terms" category, this falls under a very common and logical sequence. It's so common that to do it in another way actually doesn't work. The sequence starts with the most basic thing- a line, then adds some volume to become a form, once that form is made, it is then lit with local color, light and shadow, and finally detail is added (feathers, wood grain,etc.). Again, this is common to almost all teaching of basic art.
Now, It would be much different if someone was talking about something that DIDN"T have a common terminology or structure. For example, if you were to write about a boy wizard and named him Harry. And he was to go to a school, called "Hogwarts". Those terms are NOT common and are VERY specific to a single person's story. So you would be much more guilty of plagiarism if you did that vs. doing a book about something common, such as 2 point perspective.
The other charge is LAYOUT. Jake's layout's don't really look like AD's, but lets suppose they did. How COMMON are those layouts and is there something inherently unique that was copied? The answer is no. It's just some drawings with some text around them using common terminology. For examle, here's AD's layout and one from another pen and ink book. I could VERY EASILY say AD's was stolen from this one. In fact, I bet if I told you these came from the SAME book many of you would believe it. But it's two separate artists and two totally separate books. And if I said it with emotion, many people would believe it. But that isn't the case. AD did NOT copy this at all. It's just normal to layout sketches and text this way. In other words it's EXTREMELY COMMON to do it this way. Which makes the plagiarism charge sort of ridiculous.

