If the testing is sensitive enough to find trace amounts in the low parts per billion, then there's no "alibi"; it sounds like this is far, far below the performance enhancing level.
ppb. That's the amount of meldonium they found in Russian athletes. Far, far below...riiight.
Maybe the Russians can use the excuse that its in the water.
I think the difference with the Russians is the large-scale systematic use. It was also the same compound which suggests it was coming from the same source and although some Russians had trace and amounts, there were some with higher amounts as well. The result of which was not deemed inadvertent.