Although we'll be hosting the repository on GitHub, our contribution workflow
will remain unchanged and we will not be accepting Pull Requests at this time
So I don't know if you meant that the focus of the change wasn't GH or that they weren't using GH at all, but it seems like the latter is untrue.
They are dropping Mercurial and focusing on Git. Incidentally, they happen to host the Git project on GitHub. GitHub is used for hosting, and they don't even use basic features such as pull requests.
But a few lines later:
So I don't know if you meant that the focus of the change wasn't GH or that they weren't using GH at all, but it seems like the latter is untrue.
They are dropping Mercurial and focusing on Git. Incidentally, they happen to host the Git project on GitHub. GitHub is used for hosting, and they don't even use basic features such as pull requests.
Again, this is really not about GitHub at all.
This is the crucial detail that everyone is missing.
It's the same as with the Linux kernel GitHub mirror.