Kai basically took Ichirou's rolls when he's about to do it, suspecting he rigged it to favor him. You can see in page 7 he's making the gestures with gacha guy and that probably rearranges the balls.
ye I think coriander is right, he took advantage of it being rigged by forcing himself in and not letting that other dude get this slave. I didn't expect that but well played haha