Well they said “consumer CPU”, not “PC CPU”. So the question is, do most consumers do their computing on PC CPUs or ARM CPUs? Which then raises the question, what does “computing” mean...
Laptops outsell desktops by something like a 2:1 ratio. If you restrict your analysis to just consumer devices and exclude office PCs purchased in bulk by businesses, that ratio is even more skewed toward laptops. Desktops are a niche, and x86 could be relegated to niche status for consumer computing simply by ARM making significant inroads to the laptop market without having any uptake in the desktop market. (It's already the case that consumers tend to own more ARM-powered devices than x86-powered devices.)
Sounds a bit like Google trying to sell Stadia: "Nobody needs processing power close-by, let's compute everything in the cloud and access it with thin-clients!"
Which sounds workable in theory, but is unworkable for many people due to limited Internet access speeds/volume.
And the real disadvantage then becomes obvious when the "super powerful cloud" only renders the game at console visual details levels with in-built control-lag.
Not just limited to gaming: Video-editing is becoming increasingly popular as a hobby and a field of work, which is another use-case for lots of local processing power.
So while in terms of market size desktops might be a niche, that niche still fulfills an important function thus I don't see that going away any time soon.
