That's to do with Github not displaying PDFs very well, but if you download it you can view it fine. Also, that PDF is the Adobe Pre-Flight verification of the 5x8 template.

The sample book can be created by cloning the repo and running the container. (http://chrisanthropic.github.io/Open-Publisher-Documentation...)

If you want to see examples, I formatted everything here: https://www.amazon.com/Tristan-J.-Tarwater/e/B004WS3P3A/