The description says that the front grip broke off of the accessory rail.
he basically held the front grip tight and did not hold the gun tight enough when it recoiled he was pushing forward on the grip so hard that it broke off the gun. it actually broke a chuck out of the bottom of the Glocks receiver. the grip for a lack of better explanation was ripped off the front of the gun.
But, that guy was tough...... I would have been screaming like a little baby.
My brother in law had an accidental discharge once and shot his hand with a 9mm..... he said it was horribly painfully, and the recovery was long and painful too (and no, it was not with a Glock..... it was a SIG)