You’re missing their point, they’re saying from the point of view of those in power millionaires are middle class.

Although there are some that distinguish a “managerial class” that is in-between the middle class and the billionaires : people like CEOs and such, with net worth in the tens of millions but who are not those who benefit the most from the system and are culturally distinct. I think it’s a useful concept personally, as their interests aren’t necessarily the same as the owner class but they still have a lot of political power.