Yeah but they basically wrote their own wrapper around it, which is to say Microsoft has fallen into one of their usual patterns:

1. Picking a trendy tool

2. Mis-using trendy tool

3. Rewriting trendy tool so it's no longer trendy tool but something custom and not quite standards-compliant with it's own weird behaviors and bugs

4. Complain the standard is wrong

They wrote a wrapper around it because git took so much time for every basic operations, even a `git status` would take minutes. But still it's not a fork, you can either use it or not without impacting anyone else using the repo. And they also made it available to everyone, as how good open source citizens should do.