It looks like they just took the % of revenue each sport generates from the publically available data - Illinois does generate a larger % of it's total athletic budget from basketball vs. football than most schools, so that is likely how they came to that conclusion - basketball ticket sale revenue was actually higher than football for example a couple of years ago.
But, that doesn't mean that is how Josh will decide to use the $20.5M revenue sharing, each school can do that any way they want to, so he doesn't have to do it as a portion of revenue.