It's all stock assets, so he IS a billionaire, he just cant access those billions unless he liquidates his stock assets.
Ask Elon.
But don't bring up that Elon has the FCC on him for the billions of dollars he has gotten out of banks as loans on the collateral of his stock holdings, all the while everyone knowing that the second Elon starts selling his stock holdings, they plummet, and suddenly that collateral drops from billions of dollars to hundreds of thousands of dollars in value. Because that's how stocks work. But the rich need to have a way to make their worthless existences spend poor people's savings accounts.