Is this written by actual web browser engineers? If so, what fields did they specialize in?
I'm the rendering lead for Chrome, and know quite a lot about how it works. I also recently wrote a series of articles about the new rendering architecture of Chromium, see here:
https://developer.chrome.com/blog/renderingng/
Pavel is a professor at the University of Utah and has extensively studied CSS from an academic point of view. He also has a lot of experience teaching the material and making it accessible to students.