You have a point, and one that will lead to the deaths of many young men, as it will be used to stop the actions of high schools and colleges who otherwise would be alerted to the possibility of injury and death and would stop gladiator sports. Since CTE only shows on autopsy, and only those who think there is a problem, or their families, would allow the exam, it will be many years before the truth is nailed down. But honestly, you have to admit there is in fact a possibility that high school students who play football do get CTE at very high rates. 
The study does prove there is a massive problem. It is not faulty scientific reasoning to say if a small sample shows cancer in lifelong smokers, then cancer may in fact be caused by the smoking. The conclusion is that there is a distinct possibility of a deadly problem. 
 
Hugh Massengill, Eugene Oregon