The old Hi-standard double-action versions used to be an issue item with the LA Highway Patrol, who often carried theirs in a boot top. They at least couldn't fall on their hammer, and go off, as happened to this goof.
I recall that Lee Harvey Oswald had a similar incident while a young Marine, and he too was a Louisiana boy. Perhaps it's something in the water thereabouts.
-archy-/-
FWIW, the Ascension Parish Sheriff has one heck of a rifle and pistol range not five minutes from the Tanger Mall - I've helped out with a few Garand Clinics at the facility.
I have never trusted those stackbarrel derringers, either.