I have a 10 year old Dell Inspiron 1501 laptop with a "Ready for Vista" sticker on it running Windows 10 that says otherwise.
Indeed. It says that you did not read or did not understand the summary. This article is about mobile devices (phones and tablets) not desktop computers. Hence, the Android example and calling them "devices" instead of "computers".
Running modern OS's on old desktop hardware is not all that difficult as long as the components are popular and well supported (more obscure components may not have drivers available for modern OS's).
However, the same can not be said for mobile devices. Even a three year old phone may be officially unsupported and by five years it is pretty much guaranteed. By "unsupported", I mean that neither the preview or the current release will run. You can sometimes find hacked up versions that run on older hardware at the expense of stability, performance, and functionality. This is largely due to lack of driver support in the newer kernels for the components baked into the older devices. There is no option to chose your components wisely.