Microsoft has launched many new features of Windows. Some survive, some don't (SideShow, Gadgets to name a few). "effectively telling developers" isn't the same as "actually telling developers" which is required for malfeasance. It is also not mutually exclusive. It doesn't say "if you're a game studio and developing for Windows, we are not going to let you run your program on our OS unless you make it compatible with UWP." They're also not curtailing users' freedom, though I admit I don't even know what he means by that. Not every piece of software installed on your PC will take advantage of all features of the OS. Why would my game need to manage my drive encryption or be able to set my desktop background? Heck, some don't even care if they're network enabled.
Basically, the statements quoted, to me, do not stand up to the idea of proof. Game studios could go right on doing what they're doing and say nuts to UWP. Besides, after just a shred of thought and research, these criticisms of UWP and any technical limitations that discourage development of PC Games in UWP, Microsoft has already responded to.
The claim being made is that Microsoft will actively alter Windows so as to make alternate deployment platforms like Steam substandard and behave erratically. We are fully within our right to ask for proof of that activity being done. Besides, it seems like we're back to the age old Slashdot problem of reporting on old news.