The kid was drunk and he gets admonished for smoking pot? Good reasoning there...
I'd be really interested to find out if they actually tested for THC as indicated by the words of the judge and the report, or if they merely found THC metabolites in his system. It's a critical difference--between actually driving under the influence of pot, and testing positive for having consumed marijuana at some point in the recent past, but not necessarily under the influence at the time.
But typical.