Unfortunately it is a trait of human nature, especially amongst some of the 'less intellectually challenged', that in the excitement and tension of travel and going through security procedures, people for some unaccountable and mystical reason blurt out without thinking a 'bomb' comment. Like the kid waiting outside the front toilet of some Malaga flight when the flight deck door opened, and he was confronted with the flight crew.....'say something' the bright spark is thinking, so before he knows it out comes some stupid comment about a 'bomb'.
These people aren't the brightest sparks in humanity. I don't think they are doing it maliciously. Quite simply, they are idiots saying the first thing that pops into their head, which conversely is exactly what they mustn't say anything about!
I have seen a parallel. When one of my friends was getting things ready for his sister's wedding and the groom didn't turn up, and wasn't going to, he was running around in a somewhat agitated state. Not being a regular churchgoer, he had briefed himself not to swear in front of the vicar, obviously repeatedly. So when all hell let loose, what came out in front of the vicar? It was embarrasing, to the extent the vicar had to ask him to stop using the name of the L........... It's just one of those things in human nature!