How so? As you push the pistol into the holster it would have still engaged the trigger.
The point here is it is a worn out holster. Not because it's a glock or anything else.
On a side note I was taught to ride my thumb on the hammer as you re-holster a da/sa gun. That will tell you if you have anything caught in the trigger guard while you put it in the holster.
As well do I when I holster my XD for that very reason. Knowing your equipment is critical to safely operating it.