Luck I suppose, if you consider are the stories people have written about getting banned doing agility. Also it feels like Jagex bot detection doesn't seem to really pick up obvious patterns like that, it's more about the length of playing and taking breaks. But in the end, it's probably mostly all about luck. I did however get another account of mine a well to 71 agility with the same script but it got later banned for botting alching D: