Galco belt slide holsters are not cheap nor are they poorly made. They are made for the Glock that was shown. Whether or not it was a correct holster for his Glock is unknown. Galco, from my experience in dealing with them would most likely have sent a replacement had they been notified.
I could be wrong here but, I suspect that someone if not the owner, had softened the leather to ease drawing and it went too far. The other option is using a holster that was not correct for the gun or a combination of both.
I am totally confident that if the Galco Belt slide holster was indeed a correct holster for the model of Glock that was being used ,that this failure would not have happened.

Randy