It’s all stock assets, so he IS a billionaire, he just cant access those billions unless he liquidates his stock assets.
You didn’t read the article did you, but even without reading it you’d know he’d have to have a huge amount of income for the year (not just stock appreciation) to have a $275 million tax bill.
‘Cuban, who is also one of the stars on ABC’s “Shark Tank,” has an estimated net worth of $5.4 billion and says his tax bill is “almost all long term capital gains,” which almost certainly triggered a federal long-term capital gains tax of 20%.’
Lets assume generously that 100% if that is long term cap gains taxes (which you only get taxed on the sale of assets). In 2023 he would have had to have sold $1.375 billion in stock he’d held for more than one year.