That could be the experience of the officer in question. He relied on the tension of his closed belt to help retain the gun.
Now, he goes into the stall and wants to open his belt, but the holster will flip over and drop his gun. What does he do? Does he take his gun out? Does he hold it in one hand and do the rest with his other hand? Does he put the gun down and maybe forget it, knock it off, or kick it? Does he put it into another pocket? Which other pocket? His pants are loose and down around his knees. If he holds the gun, now he must rebuckle his belt with one hand, or assist the process with a hand full of gun.
The article is no longer there, but there are a lot of ways to drop a gun in a bathroom stall, including just forgetting that your gun will fall out. Yep, a gun retention mechanism on the holster is important. An anti-grab thumb break might not be a bad idea.