It was foolish of him to do that but then, looking at the additional link below, he was 17. It is quite possible that is never occured to him that what he was doing was unusual, not if he has been raised in an orthodox family and all his contact growing up was with other orthodox families - he was just carrying out an everyday activity with an averday item. The problem is that unlike an MP3 player (which to someone who didn't know what one was would look way more likely to be a bomb, I imagine) the other people on the flight weren't familiar with it.
The diverting the plane and landing it was a clear over reaction though, people have been watching to many media scare stories.