Conspiracy theory time: Microsoft intentionally leaked this code so they can gear up to fully open sourcing all of Windows and crowd sourcing its development and bug fixing.
It makes sense, I don't think MS cares about Windows anymore in the azure/O365 era.
It makes sense, they have very little to lose other than the glarimg issue that even with a non-free license it would inevitably end up being used to run Office on Linux via syscall or full emulation.
Maybe they're testing the waters? Perhaps there's a political problem with open-sourcing a current product that nearly every company has sunk a sizeable amount of revenue into?
Yes it is totally outlandish. This was leaked, not open sourced. No one is going to seriously contribute to a project that can't be legally distributed.