They told you wrong. The upper class is independently wealthy ---they can work like some of the Kennedys do but they don't have to. Middle class are all the people who need their paycheck, they work for an income, they work for their lifestyle which can be comfortable but when the paycheck stops, the lifestyle stops. There really isn't a difference between blue-collar and white-collar anymore ---blue collar types can make $50,000-70,000 a year and some white collar types are pulling in $20,000. The poor require charity, they don't make it on paychecks.
Which was exactly the point being made, that middle class people may be comfortable but still need to watch their budget. The description quoted was meant to be a humorous description rather then an in depth analysis of the "class structure" in the United States.