That was probably over 10 years ago now. As I heard it second- or thirdhand, he chambered a round in an M11 and then tried to thumb the hammer down instead of using the decocking lever for what it was designed for.
As you may already be aware, an M11 has no “safety” per se, but the trigger pull with the hammer down is about double what it is with the hammer cocked. So it’s not unheard of to carry one with a round in the chamber relying on that heavy double-action trigger pull as a safety.
That’s why the M11 has a decocking lever. You rack the slide to chamber a round, then use the decocking lever to lower the hammer. When you do that, there’s a blocking bar in the action that keeps the hammer from hitting the firing pin. Our intrepid CAG decided instead to put his thumb on the hammer, and then pull the trigger and try to lower the hammer that way. So he deactivated the one safety (the blocking bar) that stopped the hammer from hitting the firing pin . . . and then his thumb must have slipped. BLAM.