It takes time for substances to get into your hair. If you took something yesterday, it won't be in your hair follicle but it will be in your urine. Or the same day as the accident (since that is usually what precipitates a drug test). Regardless, the test is the property of the employer and they are not required to release the results to anyone. And even if the test was a false positive, they don't have to give this person their job back.
And if this is not YOU, then it's none of your business anyway.