It is good to be cautious but I would suspect if they were going to allow the drugs though then put you under surveillance then they wouldn't have taped up the package with customs tape and alerted you to the fact. Seems like a odd scenario any way you look at it, take precautions but I suspect you just got lucky, either that or the Nintendo's you have did not test positive for an illegal substance, or the customs person was into clubbing and decided not to fuck with your stash, all of those scenarios are highly implausible by the way :-)