Well,
This is not the first instance of people being delayed, held over or even arrested for making jokes in security. Trouble with Brit. "humour" is that it is so dry that it often sounds serious - ask my Swiss wife....
There is no room for uncertainty in the security area and what is humour for some: "Hi, Jack!" and "Gun is in my other bag" is an added problem for the checkers and must be taken seriously.
More of those and you will be an even more InFrequent Flyer methinks.
PS It happened to be easyJet but any good security system will have this philosophy.