Honestly, when I was 14 I would have thought it was cool as hell to have a realistic looking suitcase bomb if I had the skills to make one.
I am kind of leaning towards this being a publicity stunt, as a digital clock project really wouldn't require much circuitry, wiring or case space(with the result looking nothing like a bomb ). That being said I find it absurd for the child to be detained over any of it.