I think he means that of the small proportion of people who are good enough to make the NFL the coaches will have picked those that conformed to their biases.
I.E. QB A and QB B are both on the edge of joining the NFL for team C. The coach cannot pick between them and so he goes for QB A who does better on the Wonderlic test.
I.E. QB A and QB B are both on the edge of joining the NFL for team C. The coach cannot pick between them and so he goes for QB A who does better on the Wonderlic test.