WinRT is made up of component dlls and therefore exposes functional interface bundles. But the implementation of these components mostly took the path WinRT -> Win32 api -> ntdll (aka "Windows Native api" which is undocumented). But since MS wanted to push WinRT they allowed some paths to be WinRT -> ntdll. AFAIK this is what the mandate/waiver was for.
So you have the current situation that some Win32 apis have no analogues in WinRT and vice-versa. The DirectX path uses "Nano-COM" (a stripped down version of COM) which calls into user-mode runtime dlls which then takes another path to the kernel.
Lets not even get into how .NET projections/interfaces/wrappers do their job ;-)
The key point to know is that COM is only a packaging architecture/framework/middleware for structuring at a user-mode binary level.
It is all quite elaborate and complicated and so making a one-line statement like "everything is COM" is sheer cluelessness.