When the rebels enter the bunker watch the very left of the entrance and you can see the rebel now dressed as the Biker Scout and he moves into view and puts the helmet on, then stands there with his hands behind his back on guard.
I've always noticed this.
When the Biker Scout runs around the corner or the bunker after Han; and into the rebels trap; one rebel puts down his gun and walks towards the Scout. Then what follows is what I first wrote.