And as far as I know, he and his wife earned their money in tech jobs. The math is believable: let's say your household makes $130,000 a year (which I haven't done), and lives on $30,000 a year (which I've done... not fully voluntarily mind you but it wasn't hell on Earth either). You're saving $100,000 a year. In about 10 years you're a millionaire and could continue living on $30,000 forever without working. (Assuming 3% interest, which is doable without much investing effort, luck or expertise.) That's financial independence. Keep working at that point, and you only improve your lot. You can earn $10,000 a year as a full-time musician and live on $40,000. Or stay in tech and put 100% of your salary into principal while interest or dividends pay your living expenses.
Increase your monetary needs, i.e. your financial dependence, and it takes longer. Which is what most people do.