Was it? Then answering brakes question I don't believe that there was any intentional wrongdoing. Therefore, if no lab mistakes are considered it was either a misfortunate coincidence or a deliberate conspiracy to "hit where it hurts most".
See below the only negative test reported (that I'm aware of) is the Beijing test.
Yes, the statement by ROC has said that the Beijing test came back negative for any banned substance (see post #1 for the statement) Unfortunately that doesn't negate the positive test in December, the only test that i think could negate it is the Sample B from December coming back negative.