Princeps was in the car, and he saw Li Du with the police, but he was not sure about what both sides were doing.
He was staring at Li Du and the two police officers, vaguely understanding that the arrival of the police was not a coincidence. They came after receiving a tip-off, and the person who reported him was Li Du!
When he saw Li Du was handcuffed, he was elated. He thought Li Du had committed a crime too and would be arrested as well. However, Li Du was released soon.
He knew that the policewoman who had arrested him was of Chinese descent. He thought it must be thanks to this policewoman that Li Du got off. They were probably abusing their power.
The police car and Li Du side were at some distance away, and what he saw was not very clear, so he was just guessing.
