There is plenty of fault to go around.
If a person carries a concealed weapon, the authorities and the gun show producers insist that such people unload their guns before entering the show.
Then, when the person returns to their car, they find themselves motivated to be handling their gun and racking the slide while in their car in the parking lot. Unnecessary handling provides opportunities for human error.
I have found myself handling a gun in my car "unnecessarily" after leaving an anti-gun state and arriving in a state which recognized my permit. If my gun ever does malfunction, the most likely moment to find out is when chambering a round during reloading.
Driving alone occupies one's full attention. Handling a firearm occupies one's full attention. One needs to choose which.
And I never transfer a firearm from my control unless it is to that of a person in whom I know I can fully trust it with and to handle it according to protocol.
William failed in both areas.