There is no way any one will fire a revolver or double action only firearm twice accidently. Even once would seem a remote possibility given the length of trigger pull on most of them. Letting it drop would have been the safe thing to do. My bet is it didn't happen the way he says it happened.
I can see how it would be possible to fire two rounds from a Glock. The first round as your finger caught on the trigger, and if you're finger caught in teh trigger guard, the second round could have been from flinching when the first went off.
Possible? Sure. Just really, really unlikely.
I agree that the story sounds concocted to cover an even worse mistake.