This looks like more data towards the "LLMs were involved" side of the argument, but as my other comment pointed out, that might not be an issue.
We're used to errata and fixing up stuff produced by humans, so if we can fix this resource, it might actually be valuable and more useful than anything that existed before it. Maybe.
One of my things with AI is that if we assume it is there to replace humans, we are always going to find it disappointing. If we use it as a tool to augment, we might find it very useful.
A colleague used to describe it (long before GenAI, when we were talking about technology automation more generally) as following: "we're not trying to build a super intelligent killer robot to replace Deidre in accounts. Deidre knows things. We just want to give her better tools".
So, it seems like this needs some editing, but it still has value if we want it to have value. I'd rather this was fixed than thrown away (I'm biased, I want to learn systems programming in zig and want a good resource to do so), and yes the author should have been more upfront about it, and asked for reviewers, but we have it now. What to do?