I have to assume they meant 79% of US consumers who use iPhone, since only about 60% of the US uses iPhone, and Carplay specifically is useless to the remaining 40%.
Or perhaps they were grouping in AA under the covers.
Well, it does seem like CNBC is the source of the stat and they do not say it like that. One could make an inference since the previous sentences mentioned new cars.
I don't think I can find a source that supports your claim that iPhone users are over-represented in that group. There was a period where income matched what phone you bought, but these days an older iPhone is pretty cheap to acquire, and the network effects mean people are willing to spend more to be in the ecosystem.
Assuming income as a proxy, from a bit of research it seems that in 2022, 56% of "high income" earners claimed they owned an iPhone. So that split is getting a lot closer, but this is already less than the 60% we have already established Apple has in market share across the US, so that doesn't exactly support the 79% figure. Other sources show about 55%-56% iOS users in the US during that period.
To be fair, I can't see what high income actually means in this data.