I think most weapons, especially modern handguns, unless the trigger is held, the firing pin is retained or blocked. Free-floating firing pins are old and not in use today.
Remember, the cowboy of old with his western six-shooter didn't have a round in the chamber because it might go off if the hammer was hit.
If the free-floating firing pin was still a factor, then people today would not have a round in the chamber under the hammer.
Something doesn't sound right. . .but maybe the firearm experts here in FR may be able to offer more info.
Guy was bored, so he tied a string to the trigger and used the pistol as a yoyo. He was trying to walk the dog when it went off.