It's openly acknowledged in the published material: "OpenAI ChatGPT generated text for this book. The editor provided direction to generate prototype text for each topic, then edited all of it by hand for clarity, correctness, coherence, fitness, and the like."

Yes. I generate a topic then edit it. ChatGPT text comes out similar-enough to my own writing style, meaning summaries then bullet lists, that using ChatGPT feels a bit like a really good autocomplete.