It's almost as if there's only really 2 classes and most of the population don't know anything about it. They define it by arbitrary things like the ability to shop at M&S and Waitrose rather than their relationship with the means of production.
An accountant may earn much more than a shop assistant but they're both still dependent upon their labour for their income. If they can't work for some reason they both still risk poverty. One can afford nicer things, sure, but they're still of the same class. The middle is a lie created to make some feel superior to those below. To create a divide, to buy off the more educated proletariat, but it is still just a lie.
That's why, according to the article, what they define as the working class hasn't changed. The capitalists have by and large only got richer, they're not dropping in standing. Whereas the made up middle is finally learning which class it truly belongs to.