He says "They're treating me like someone who broke the law." Dude, that's because you did.

This guy is trying to shift the blame to everybody but himself. He failed to register with the police on a previous trip to China. That's the source of his problems. How would Air China at Seoul even know he had that issue in his background? TIMATIC isn't going to reveal that about his particular case. Why wouldn't Air China have let him board? He keeps referring to this being a "new law." You or the place where you stay have always had to register when you travel to China. Of course, failure to do so is going to cause you problems when you come back to China.

China's TWOV is quite generous, but if you have something in your background that violated the rules, you're not going to be able to use it.