that total drug seizure amount most probably includes what security found. they would have simply confiscated in most cases.
in the middle of a festival, with people and potential trouble everywhere, i can see cops finding small amounts of drugs and not arresting the person(s). do you think they're going to arrest every joint smoker at camp bisco? an arrest = several cops out of commission while they take evidence, fill out paperwork, transport the suspect to jail, make a statement before a magistrate, fill out more paperwork...
i do agree that a large portion of the haul was with those 7 arrested... just not all.