To my mind although Buffett won the bet on the terms as agreed at the start, he disproved his own contention.
The initial stake was $320k each invested in bonds. By the half way stage this $640k had grown to $1m. Which was the agreed amount to be given to the charity. It was then agreed that this $1m be invested in Buffett's Berkshire Hathaway's B shares. Buffett guaranteed the $1m stake.
This grew to $2.2m over the remaining term beating both the Hedge Fund and the passive investment.
So a stock picker, Buffett, actually beat the broad based passive investment.