Lets just say it is 2nd hand he should still get some kind of punishment for being an idiot. You know you have a history with failed tests and then you are hanging out with people who are smoking? And for you to inhale enough for it to show up on a drug test you basically have to be sitting in a car with the windows up or "hot boxing." DUMB!
I think more likely is he used a while before the test and it was almost out of his system so it only showed up as a small amount. I can't explain the different results but I still don't believe that this was just 2nd hand especially because this isn't his first failed test. He has a history.
A lot of people go for the 2nd hand smoke defense but it is compete BS. It is almost impossible to fail a drug test if you didn't actually use the substance. It never works. That is what I call "reaching."