Chen Fangmiao couldn't be completely innocent given what he did.
He was a student, so it was strange that he carried a knife with him. Therefore, Du Jialei's parents refused to believe that Chen Fangmiao was just impulsive. He might have had the intention, but lied after being caught.
Du Jialei's parents didn't doubt his words. They were always aware of the Chen family's ambition and were worried that they might hurt Du Jialei, so they stayed alert. Moreover, there was no reason for Du Jialei to frame Chen Fangmiao. They knew Du Jialei's character better than anyone else.
Du Jialei also said that Gu Ning had saved his life.
Although the Du family wasn't a super-rich family, they had heard of Gu Ning because they were involved in the business too.
So since Du Jialei mentioned Gu Ning, he wasn't afraid if his parents went to ask Gu Ning about that.
