What I understand is that you absolutely lied and said he was "starting to stand up when his arm broke" when he was still down on the ground. When I pointed out that you lied since Jack's pathological lying is rubbing off on you, you quickly changed to "Right before that clip starts Mir had been face down, Sylvia was getting up."
You're also confusing "perfect" with "common." It doesn't happen often, but when you have someones elbow in your crotch and you yank on their arm in the opposite direction, it puts pressure on the forearm and it can accordingly break. Just because it's not a common occurrence doesn't mean it was lucky or that Sylvia was "slipping out." Mir has a lot of somewhat bizarre but devastating submissions that are incredibly rare. That doesn't make him lucky, it makes him unique. Jack, much like yourself, also confused the two instances of when Sylvia was legitimately slipping out and when Mir re-adjusted and locked in the submission. Sylvia wasn't slipping out, and it wasn't luck. It's really that simple.