I think the point here is that Aviation Security are to some degree reliant on a passengers verbal confirmation that they have nothing in their baggage that is dangerous or illegal to bring into a country, and so long as we have idiots who be sarcastic about the process, then its wasting AvSec time. But in all fairness, if some fool (like this guy) leaves his bags unattended, and then returns to the bags accompanied by AvSec stating that there is a bomb in them, you cant blame AvSec for arresting the guy.
Imagine if it was some loose nut who did actually have a bomb, and when the passenger makes a statement that he has a bomb security just shrug it off, and then the airport and all the passengers are blown to bits. Then AvSec are in the firing line.
You cant tell me that just by making a spot-assessment of the passenger that you should be able to tell whether they're a terrorist or not and then alter the security process based on your own judgement. Where other people's lives are involved, security must be taken pretty serious.