They acted on the medical advice they were given, so i'm not sure why you think they 'fucked up'.
The woman who was subjected to the inquisition by the BBC, explained that the IAAF doctor had been told by the athlete that he'd started vomiting at 10pm the night before.
Either you believe the doctor, who had no reason to invent the story, or you believe the athlete who had a very good reason to change his story.
The athlete had all the symptoms of the virus and as she also explained, it takes 48 hours to clear the system, regardless of whether he felt well enough to compete.
They couldn't do all the tests because by the time they had the results, he would have competed and potentially infected a whole load of other people.