Looks as if they could have provided some actual statistsical comparisons to the general population rather than that general statement.
And they didn't start playing pro football, or football in general thirty or forty years ago. Pro football started well before WWII. The first pro football players have died of old age. Looks like there'd be a fair sized population of former players to study and generate stats from.
Lots of assumptions and generalities and not many well supported facts.
Back when football players were 5’10”-6’2”and 180-220 pounds, and not propelling themselves into each other quite as fast, the impact of the collisions was less.