Shooting at Airport

The traveler thought the Glock semi-automatic pistol was unloaded, but there was likely an extra round in the chamber

There are no extra rounds in the chamber, never more than one, this idiot failed to clear it before arrival, lucky he maintained safe direction, but just had to put his finger on the trigger.

"All Guns Are Loaded!"

You never think they are unloaded, you ether know they are loaded, or know they are unloaded.

"Always keep your finger off the trigger until the sights are on target, and you have made the conscious decision to fire"

It is simple just keep your finger outside the trigger guard untill you have decided to fire the firearm.