Because it's well known by anyone interested in this area? There's been a barrage of "Windows 10 Telemetry/Privacy" related stories since its release. It's also publicly documented by Microsoft itself: https://technet.microsoft.com/en-au/itpro/windows/manage/con...

"Performance and reliability data, such as which programs are launched on a device, how long they run, how quickly they respond to input, how many problems are experienced with an app or device, and how quickly information is sent or received over a network connection."