Your "false alarm" could have been from some moron putting his shoes on the sampling table.

They should never remove items from your sight, though.

Think of this being more akin to a car alarm, they go off all the time and nobody is up to anything. It just makes people take a closer look. They should have explained the situation to you, but I think it has become so routine for them, they forget the customer service part.

If you actually had anything to worry about on your next trip, they probably would have had more alarms. Just a side note, some of the compounds in certain heart medications are similar to what is being tested for. If you, or someone in your immediate family takes these, you may want to mention this should another alarm occur.