As stated in the guide (chapter What am I trying to achieve?:
[…] take a fresh Raspbian installation, do some hardening, install git […]
Means I just install and configure the Git apt package and no additional Git-server software. GitLab, etc. bring additional functionality, which, for example, make it easier to build an Continous Integration workflow to automate builds.
If you run my little project you just get a dedicated (and private) machine to / from which you can push / pull local Git repos.
You can find a more detailed explanation of for what I personally use this little machine in this post: https://community.openhab.org/t/setting-up-my-own-git-server-on-a-pi