The event happened years ago (pre 2007). It is not a "spontaneous discharge" but an accidental discharge due to impact. 1911s have the ability to discharge when dropped unless modified with something like a firing pin safety. Series 80 Colts have this, but the Colt in the incident did not. The gun impacted on the muzzle. Inertia drove the firing pin foward through the tension of the spring just as would happen if struck from the rear by the hammer, resulting in the discharge.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011