What evidence in the article supports the claim that the PC backwards compatibility layer uses Xbox 360-era code?
The article states Microsoft’s Xbox app uses the Xenon Fusion, aka XeFu, emulator that was first implemented in the Xbox 360, and that Windows PCs load an Xbox 360 environment before running XeFu to emulate the original Xbox. It cites a discovery by Twitter user TheLunarixis who found XEX2/STFS signatures and kernel strings such as "XENON KERNEL EXITING" as confirmation of the 360-era code being used. Answered
Could this PC backwards compatibility approach allow Xbox 360 games to be brought to PC in future?
Yes. The article states that because Windows loads an Xbox 360 environment first and then runs XeFu to emulate the original Xbox, this approach implies Xbox 360 games could come to backwards compatibility on PC at some point. However, the article also makes clear that nothing has been officially confirmed. Answered