I don't think that's what they meant. There were 70 alarms that turned out not to represent terrorist threats. Some of these might have been false alarms, some might have been unregistered equipment (illegal, but not connected with terrorism), some might have been legal shipments improperly shielded, etc.
In situations like this, one prefers to be cautious; one would rather err on the side of false positives than false negatives.
But this event has happened 2 months ago and nothing but the sensor has been discovered. Two days too late to catch the goods.