I'm thinking it's a combination of the saddle did not fit + was too loose in addition to the initial bolt. Even with a loose girth a western saddle shouldn't be sliding around. I'm guilty of stepping off my horse at the end of a ride and seeing air between the girth and horse before.
If the saddle doesn't fit, shoving your weight over, in addition to the possibility of throwing him off balance, pinched him somewhere, making the situation worse.
That's what ORS's are for, getting an out of control horse back under control. However, there's more to it than the actual stop, the horse needs to be disengaging their hindquarters as they circle down so they can mentally come back to you. If they do NOT disengage behind they are still mentally and physically prepared to still bolt, rear or buck. Horses that don't disengage during a ORS are the ones that can become ones that rubber neck and are still misbehaving, just with their head to the side.
The important thing however is to respond quickly, you need to bend the horse down gently ( not just yanking them around, that can make a horse flip ), and spiral them down to a stop.
But yes, it does work on panicked horses, about a month ago I was riding my project mare out for the first time, all in the span of about 30 seconds, a big rig came past blowing their horn, ALL of the barn dogs and neighbor dogs starting aggressively barking at it, the horses nearby spooked and bolted in their pastures and the neighbors started a bonfire with screaming kids. Poor project mare, Cookie, lost her marbles. We went from a relaxed trot to gallop in a blink of an eye and was gearing up for a real bolt and buck. I brought my hand out to the side and I hadn't even taken the slack out of my rein to her halter and she spiraled down immediately. However, ORS's are something I school every horse I ride on and they're second nature to me. If I had been a few moments longer, I know I could of gotten her stopped but not near as quickly.