Having not looked at any of the files yet, I wonder if it's just the changes that were made to WinXP for Xbox-use. IIRC throughout its' history the Xbox OS has just been a modified version of whatever version of Windows Microsoft is pushing at the time, with the OG Xbox being based around WinXP.

I'm very curious to see more come out as the code is picked apart piece by piece, and whether or not it'll confirm my suspicions. I'm also very interested in that Xbox folder, with any luck it'll be time to dust off my old OG Xbox and do some hacking!

AFAIK, the original XBOX was always based on a heavily stripped-down win2k kernel, and evolved very little. The "API" games used was a jump table to kernel functions, everything ran in kernel-space. I don't know much about later consoles, but I wouldn't be surprised if they used the same generic architecture.

https://xboxdevwiki.net/Kernel that site has quite a bit of info, with ongoing reverse-engineering and clean-room reimplementation projects (reactos, xquemu)

reactos being clean is a funny joke