To be fair the write-up on that page is not the clearest possible. I think nostr:npub15qydau2hjma6ngxkl2cyar74wzyjshvl65za5k5rl69264ar2exs5cyejr may be working on a better protocol description.

The idea as far as I know is just that there may be many Git servers anywhere -- like Blossom servers -- that host repositories from anyone (maybe they'll ask for a pre-payment, maybe they will have a free quota for some Nostr users and so on) that you can just push your repositories to. And your pushes are pre-authorized by publishing a Nostr event beforehand that says what is your repository state (branch=commit, HEAD=branch or something like that).

Then when announcing your repository you can include multiple git+http URLs to these servers that people can clone the project from. And Git-enabled Nostr clients can contact these servers to download and display source code and Git history data.

It's a very simple idea but a very powerful one.