Eh, that's been a thing for a long time. Decades at least.

I think that the problem is that there isn't really a great term to clearly refer to the "non-monitor-and-peripherals" part of the "computer". "Case" would refer to just the case, not what's in it. "Tower" or "desktop" is overspecific, refers to particular form factors. I have a tower, but some people have under-monitor desktops (though that's rare today) or various times of small form factor PCs. If I say "computer", that doesn't really clearly exclude peripherals.

And honestly, we don't really use the term "GPU" quite correctly either. I'll call a whole PCI video card a "GPU", but I suppose that strictly-speaking, that should only be talking about a specific chip on the card.