There might have been a considerable rotational energy left, though, and, say, an edge of the rotating bullet caught the glass just right.
I had plausibility issues with it, too, though, when I first read the thread. Did anyone report a ricochet "whang" when it happened? Have the people present at the time been questioned?
Any pix of the broken/cracked glass? Maybe the glass was just about ready to let go from stress-cracking when it got tapped by the bullet.
Terry, 230RN