Given that a bomb in the hold is going to make as large of a hole as one in the pax compartment - and that it would seem easier to check carried-on devices (by turning on, if nothing else) than to check items in the hold.... Assuming that this isn't entirely political, then maybe whatever intelligence they've received isn't explosive related?
My initial thought was a weapon of some sort (gun, knife) hidden inside the laptop - but it seems unlikely that you could get much inside a tablet. That leaves a question of software. Could terrorists/hackers have found a way to use a laptop to interfere with communications or the operation of the aircraft? If possible, it would probably require "hands-on" the device, which would be impossible with it in the hold.