This is a tutorial style book, rather than an 800-page manual reference. It helps the beginners to understand the big picture of Kubernetes in 1-2 days. Whether or not it is a good style, it depends on tastes. I prefer this style because it helps me to get started and gain confidence fast, really fast.
Yes, this book is written in the colloquial style, lacking formalism in a typical technical book. But the question is why is formalism essential for every book? If this book helps beginners, why do we ask for formalism? Is it because we "believe" every technical book is supposed to reach a certain level of formalism?