If he "truely" wasn't doing any drugs they will be able to tell with a GC/MS test on the sample. If he wasn't doing any drugs he should request they do that test on his specimen. Anybody can fire anybody for any reason. Most companies have a dept for drug addiction but if you talk to them before you get into trouble they'll usually tell you its just for show. They fire anyone testing positive. But it sounds like his company may be one of exeptions.Work with them and see where it takes you.