Yuan Chonghuan had indeed let out a scream during the process of being dismembered. According to the records, he had been cut 3543 times until his skin and bones were gone, and his heart and lungs were screaming non-stop for half a day. This indicated that Yuan Chonghuan had screamed when he was executed.
I really can't answer that. It's possible the name wasn't clearly stated or it's a very specific detail that's hard to remember without more information.
One possible reason could be a misunderstanding. Maybe a character in the fanfiction misinterprets Namjoon's actions. For example, if he was trying to do something helpful but it came across as interfering. Another reason might be jealousy. If Namjoon is achieving great things in the fanfiction world, other characters could be envious and lash out at him.
Another way he could react is with resignation. If he realizes that the person yelling at him is not going to listen to reason, he might just let them yell and not fight back. He could simply look down, shoulders slumped, and wait for the yelling to stop. This could also show his maturity in the face of unjust anger.