He explicitly says that right before? "4/ For example, our inflation-adjusted data say car prices have not increased since the mid-1990s."
I believe his argument is more around how we're calculating inflation, i.e. that prices have actually gone up more than economists claim through inflation. Looking at inflation adjusted numbers in the fifth thread would lead to circular reasoning and is besides his point. That said I am not great at dissecting these kinds of twitter threads and may be misinterpreting too; I agree that the way he is arguing it is confusing.