Well, the fact that the police called in bomb disposal, and they also deemed it suspicious enough to carry out controlled explosions means that clearly they thought it was pretty serious too.
Also, this was hold baggage, and the equipment used to screen hold baggage is far superior to the hand baggage process, such as 3D scanning and interpgral trace detectors and such, so, it takes a lot more to 'call it in'.
End of the day. This is what security is there to do, detect suspicious items. Very easy to speculate on how to do a job better from an armchair when the full facts are not known, isn't it?