The UFC arranged the fight. USADA flagged him for whatever reason. The test wasn't going to stop the fight, it was just going to possibly factor after the fight. He's saying he doesn't want the fight if it's tainted.
It goes to show how stupid this **** is. He was exonerated because they were able to trace the source. Guys have their legacies destroyed when they can't find the source. Guilty until proven innocent.