The next level above financial independence is financial freedom (you can just get whatever you want, from shoes to houses) - off the top of my head I would guess this is probably around the 0.01%, which would be about 32k people in the USA. As an example of freedom, these people can buy nationality and avoid immigration limitations (going rate is ~$1-5m).
The article is way off just comparing salaries. There are 3 social classes in terms of having a meaningful lifestyle distinction - those who have to work for someone else, those who don't, and those who have full freedom to decide where they go and what they do each day. All they did was compare a bunch of people in the same social class (somewhat shockingly the Romans considered this equivalent to a slave class).