Windows CE was ported to a lot of processor architectures at that time. Its architecture is quite different from the Windows NT line. To quote Wikipedia on this
> https://en.wikipedia.org/w/index.php?title=Windows_Embedded_...
"Unlike Windows Embedded Standard, which is based on Windows NT, Windows Embedded Compact uses a different hybrid kernel."
I am also pretty sure that Windows CE's architecture is quite different from the OS running on the XBox, but cannot give a quotable source on this. At least for the Xbox 360 and XBox One, I am pretty sure that I have read that their kernel is actually not so dissimilar from the kernel used in the NT line. The difference between the Windows NT line and the XBox 360/One OS rather lies in the software running above the kernel.