Interesting that they put this in a Git repo (instead of TFS), but only to then push it to CodePlex (instead of Github)
Considering Team Foundation Service, project Kudu/Git deploy on Azure etc. it makes sense to think that Microsoft are making a play to seriously take on GitHub and Atlassian, so that they're the one provider that owns an entire software ecosystem, end to end.
Either way, I don't think that the EF team would have had a choice on where to host it...