It appears the author is leveraging Fabien's branding by copying not only the style of post but more importantly the formatting and style of Fabien's books. Even structurally the book appears quite similar.
If you didn't double check the author while skimming this Keen book, you may well be mistaken that it was written by Fabien. This doesn't sit well.
I took a quick skim of the content, it looks great - tempted to purchase a copy to support the author for their efforts (and have it sit on the bookshelf next to two other very similar looking books...) but need to sit on this for a while.
Maybe I'm overthinking this. Would like to hear Fabien's take on the situation.
"...I discovered Fabien Sanglard’s website and began reading his Game Engine Black Books on Wolfenstein 3D and Doom. Inspired by those works, I wondered whether I could do something similar for Commander Keen: open up the source code, explore the files, and piece together a picture of the overall architecture and the clever tricks used. The style, dimensions, and structure of this book are intentionally similar to Fabien’s Game Engine Black Books, as an homage to those masterpieces. To give it a personal twist, I inverted the title and cover to white."
We consume his site for the content, not for the minimalistic design that exist since the inception of the universe.