For books that are published in more traditional manners, digital or paper, there is normally a credible publisher, editors, sometimes a foreword from a known figure, reviews from critics or experts in the field, and often a bio about the author explaining who they are and why they wrote the book etc. These different elements are all signals of reliability, they help to convey that the content is more than just fluff around an attention-grabbing title, that it has depth and quality and holds up. The whole publishing business has put massive effort into establishing and building these markers of trust.
This source is really hard to trust. AI or not, the author has done no work to really establish epistemological reliability and transparency. The entire book was published at once with no history, no evidence of the improvement and iteration it takes to create quality work, and no reference as to the creative process or collaborators or anything. And on top of that, the author does not seem to really have any other presence or history in the community. I love Zig, and have wanted more quality learning materials to exist. This, unfortunately, does not seem to be it.