Edit: I see the original poster has edited his comment to remove his statement that this is just what software emulation is, but I’ll leave my below response as it was.
That’s not quite true here, as the Xbox Series X uses the same hardware architecture as the Xbox One, so this isn’t an instance of requiring hardware built in or full on emulation to run past titles. This is much closer to a PC continuing to run games as you buy a new CPU and GPU.
As evidenced in the article, there is no patch being downloaded to make these games run after connecting to the internet. It connects, it boots, it runs. As stated, there is the potential that there is an invisible configuration file being downloaded in the background, but there is no evidence of that.
So yes, this is different to what occurs when you chuck and Xbox or Xbox 360 disc into your Xbox One, where the system wasn’t build to support those older platforms in the first place and new software emulation had to be built which required a full game download for compatibility.
