But it should not be unexpected for the number to be higher. For years people who weigh hundreds of pounds are hitting each other repeatedly. And they are paid considerably well for it. Plus, we should compare this to other sports as well, as even most non-contact sports (soccer, basketball, even baseball) have collisions from time to time. Football should have a higher percentage than those, but without knowing the percentages in even 'safe' sports, these numbers are practically meaningless.

The real issue would arise if they can somehow test high school students and find similarly high percentages (90+ percent), but since you can't test right now until they are deceased (from what I understand), that would be extremely hard to do.