What is the right course of action now?

Your answer is fully correct. In this situation, when another driver behaves unpredictably or dangerously—such as signaling a turn contrary to their lane position—it is important to ensure your own safety first and alert others to the hazard. Warning the driver by sounding your horn and flashing your lights helps draw their attention to the mistake and can prevent an accident. Moving as far to the right as possible creates more space between you and the danger, reducing collision risk. Notifying the police is also appropriate, as it helps authorities become aware of dangerous driving behavior that may need intervention to protect other road users. This combination of actions follows German traffic safety principles emphasizing caution, clear communication, and involving law enforcement when necessary.