What is the right course of action?

You chose the correct answer: you have to wait. According to the right-before-left rule ("Rechts vor Links") in Germany, priorities at intersections without traffic signs or signals are given to vehicles coming from the right, even if they are motorcycles. In this situation, the motorcycle is coming from your right side and has priority. Waiting is the correct action, so you handled this scenario right. Always remember: at intersections without signs, give way to traffic from your right. This will help you safely navigate similar situations in the future.