This book is not a technical bible or the ultimate authority on how to use design patterns with Unity, and it's best described as a guide filled with design propositions to resolve some game programming challenges in Unity. The code examples included in each chapter are not flawless implementations because the art of design and programming is a continuous refinement process, and so the core goal of this book is to introduce you to potential solutions and inspire you to find better ones.
I always recommend seeking at least two sources of information on any technical subject, particularly concerning design patterns. It's essential to avoid getting too influenced by a single perspective of a complicated subject matter to the point that it becomes dogma instead of knowledge.