That criticism seems pretty tangential to BYOL's stated goal of learning C.
> This book is for anyone wanting to learn C, or who has once wondered how to build their own programming language.
which I interpret as having "design a language" as another goal. Arguably the book succeeds at building a programming language, but it mangles the theory in unhelpful ways, e.g. lexical scoping isn't a static analysis per chapter 16, nor is parsing the consumption of an abstract syntax tree per chapter 10.