This is one of the least believable defenses on the level of "Affluenza", anyone who has ever handled a gun in their life know they don't just go off.
..... I wish this was true. At least there is something here I can understand.
Maybe if you have only experienced double action only, or even double/single action if you arent familiar with cocking the hammer yourself, making for a long and heavy first draw.... So this would seem bizarre, as you really have to apply pressure to double action as it raises the hammer when the trigger is pulled. takes about 10+ lbs of force (The sidearm I am most familiar with, requires 13 lbs of force for double action, it also has so many safety features they are touted as 'redundant' and still, nd's can happen if you aint on it) to get the trigger to move and it has to be depressed from its at rest position all the way to its firing position, with that consistent amount of force the whole way.
However weapons with single action, or both modes, have a trigger pull weight of 2-5 lbs, which is very very light, hair trigger is a good description, as in if a hair falls on it, it will fire. Not only is it much easier to pull, but the trigger position is already right up to the point where if it moves at all, its firing. Since you have to manually raise the hammer, the intended use is you are going to use deadly force. Not a show of force, not a deterrent, you have positively identified a target as one you are going to kill, as in they are already an active shooter (a real active shooter actively shooting), or have directly pointed the weapon at you, or other people. The light trigger mitigates accuracy impediments like trigger pull, firing anticipation, and pull/firing lag, the errors associated with these can be magnified exponentially with an adrenaline rush. Even during scoring ranges, my finger was never in that trigger well, and the weapon was never on fire, until the exercise started. cocking and flipping the safety was just too easy and can be done with the trigger hands thumb while aquiring a rising target, so there is zero reason to have a weapon on fire, or a hammer cocked unless you have decided you are going to kill a threat (a REAL threat). There is a reason safety-less weapons are frowned upon, they have little to no time saving value, and a whole laundry list of deadly cons.
So if this weapon was wrapped up, loaded with a round chambered, and that hammer was cocked, or somehow got inadvertently cocked while packaged which could easily happen during handling, just about any bump or tap that could push any packaging into that trigger well, would set this weapon off.