The drug argument needs to go back a few years, because when Cooper was 14 he ran one of the fastest 400m times ever in the US for his age (48.7, less than one second slower than Quincy Wilson's age group record). He also crushed the nation's middle schoolers in the 800 meters, meaning that he had both elite speed and elite strength.
That's the profile of a kid who could become a very special 800m runner. So, I think if the argument is that he couldn't do this performance clean, the argument implicitly is saying that he was doping as an 8th grader.