If I understand this correctly, Valve provides the src packages for the packages they distribute. This person wrote a script to download the src packages and extract them. The README misleadingly claims it's a "mirror" of Valve's private git repos, which is not accurate.

The author wants them to open up their GitLab instance, showing their internal development. That's not required under GPL.

Valve appears to be complying. This person wanted access into their internal development systems, though.

The rest of the README is tens of thousands of lines about capitalism, abstaining from procreation, and withdrawing from society with hundreds of links to videos and hundreds of quotes. It's very strange. These are not the writings of a healthy person, sadly.