AP argues that because of income disparities in different parts of the country, defining working class by educational background instead of income makes sense. A $50,000 family income in NYC is practically peanuts. $50,000 in Dubuque is a lot more.
Yeah, I'd guess that was probably the reason given. The problem is that this is not a geography of class:
Even if class is a factor in it. Another problem is the tendency of people to lie about their qualifications. In most countries the effect of that would be obvious, but I wonder if it might work the other way in America, given post-1960s anti-intellectual discourses*.
That said given that non-working class people who are prepared to admit that they don't have a degree are likely the staunchest in support for today's Republican Party, any significant
movement amongst whites without degrees is probably related more to movement amongst working class voters, rather than the others.
*Often promoted by... er... intellectuals. But then, hey. Engels was a capitalist.