I'd be surprised if none of their employees have contributed to Git. I didn't interpret anything in the article as saying that GitHub develops Git, in its entirety (or even largely).
> GFVS is a GitHub project
GFVS is a Microsoft project and GitHub seems to be contributing. And the GFVS developers have been submitting, successfully, their changes to Git itself upstream to the actual Git project. So it is becoming a part of Git.
In git.git, there are 7 commits with @github.com authors, last one from 2014.
(I hope it just means GitHub folks are trying to blend into the crowd by using personal addresses, or something...)
> Shortly after our initial deploy, we also started the process of upstreaming the changes to Git so the whole community could benefit from them.
Source: https://githubengineering.com/counting-objects/
But I guess most of their git related work time goes to libgit2.
Jeff King (peff) has worked for GitHub for a long time:
https://github.com/git/git/graphs/contributors
Michael Haggerty (mhagger) is also a GitHub employee.
So, yes.
"Microsoft [...] wanted to get these modifications accepted upstream and integrated into the standard Git client.
That plan appears to be going well. Yesterday, the company announced that GitHub was adopting its modifications and that the two would be working together to bring suitable clients to macOS and Linux."
This hints that Git upstream = GitHub. I mean, why mention GitHub at all if they aren't upstream? The rest of the article doesn't explain GitHub's role in this story either.
Microsoft made some contributions and they're working to get them accepted upstream. They're maintaining a fork basically.
GitHub is adopting their modifications, i.e. GitHub is running Microsoft's fork.
Microsoft's modifications are necessary for them, particularly so they can use Git with the giant Windows repo. Presumably, GitHub also has a need or desire for those same or similar modifications. IIRC, some of GitHub's largest customers need or want a version of Git that can also handle large repos, or repos with large files or large numbers of files.