Well, in theory it just means that owning money is a leisure activity for these people. People like spending money on leisure. According to Austrian economists interest rates simply represent people's time preferences. For some strange reason they believe that interest must be positive because time preference is always positive (people want things now instead of later).
They clearly ignored that people might want money/capital (not things) now and things later. If that were the case, then their time preference would be negative and it would also mean interest rates must be negative. So even by the weird Austrian economics logic interest rates must become negative as more billionaires accumulate capital for the sake of accumulating it, rather than for the sake of production.