I've got one of these revolvers.... must have a 15 pound pull on double action! About impossible to have an "accidental" discharge in the manner described UNLESS the revolver was improperly holstered and SOMETHING with some mass and strength got in the trigger-guard.
Now, with the hammer back the pull is MUCH lighter. But IT STILL AIN"T GOING OFF UNLESS SOMETHING GETS IN THE TRIGGER GUARD AND PULLS THE TRIGGER!
My "guess" is that the guy had it in a waist band OR JUST IN HIS HAND and with the hammer back as he played and then he sat down with a thump on his rump with is finger on the trigger and he heard a HUGE boom. Strange-- no mention that I saw in the report of damage to any furniture LIKE THE CHAIR HE WAS "SUPPOSEDLY" SITTING IN WHEN THIS HAPPENED.
Even if the hammer was back and by some chance the holster caused the trigger to release it, the trigger has to be fully pulled back to pull the "hammer block" out of position so the hammer can fully drop and fire the round. Likewise if the thumb was on the hammer.
For those that aren't familiar with modern revolvers, take an unloaded one and look through the gap at the rear of the cylinder. Shouldn't see a firing pin with the hammer down. Now, cock it, put your thumb on the hammer and by pulling the trigger all the way back and holding it, when the hammer is released you will see the firing pin between the "breech face" and the cylinder, through the gap. When you release the trigger then the firing pin will be retracted. This is a safety feature many manufacturers, especially S&W, use to keep the firearm from discharging when there is no finger pulling the trigger fully back. This is similar to the firing pin lock on a semi-automatic pistol although the operation is different. This "safety feature" became pretty standard on revolvers after some "Homer" in Texas shot himself in the leg and then sued Ruger.
There are no "what if's" in this case, the dude had his finger on the trigger. If the gun WAS in the holster, the side-blast from the gap between forcing cone and cylinder is enough to blow out a chunk of meat, not to mention the muzzle blast. He's not only real stupid, but also real lucky.