The bet was made in 2007. A Random Walk Down Wall Street [0], considered the book that makes the case for index funds over a hand-picked portfolio, was published nearly 25 years earlier (1973) and was sufficiently well-known to qualify as common sense. Though there are still plenty of investment managers that are motivated to claim otherwise.

[0] https://en.wikipedia.org/wiki/A_Random_Walk_Down_Wall_Street