If you're talking about the transition from Wardoff Right to Rollback, then the initial rightward shift of the right arm is to change the contact point with an opponent's arm. In Wardoff Right, the right arm's contact with the opponent's hand or arm is in the radius. To roll back, you need to rotate your arm around the opponent's, changing the contact point in your arm to the ulna side. Here, the "roll" begins, and as you shift your center of gravity back to the left leg and turn the upper torso leftward, the right arm concurrently rotates counter-clockwise, providing a rolling surface for the opponent's advancing arm.
In solo form practice, some people exagerate the right arm's initial shift to the right, while some merely open and straighten the arm slightly. In push hands, the transition begins to feel quite automatic, so that the right peng hand changes easily to a standing palm, seated-wrist orientation.
Tell us more about the interesting things you saw. Rollback is full of possibilities for unbalancing, immobilizing, summersaulting, bouncing, tossing, or duckwalking an opponent.