It is amazing how an honest human mistake can shut down an International airport for 12 hours.
You've slightly misunderstood. No mistake. The news report states the boxes were found, suggesting that they magically appeared from somewhere. As I understand it, they were off loaded as normal and then noticed to be "suspicious".
There's something I'm missing though, 'cause i can't understand why it would take took 12 hours to clear a fairly regular occurrence.