It wasn't Chen Meng'er's analysis of what the Qu family would face if the people from the Lu family were acquitted that made Elder Qu make such a choice.
Instead, it was a thick stack of paper and a small notebook that Chen Meng'er took out from her bag before she left the study. And before Chen Meng'er left, she left behind a sentence, "Grandpa, the Qu family's rise is not only for the Qu family, but also for the Green Gang. It's also for this country. Take a good look at the information here. When you're done, come and tell me your choice. If you're done looking at the information and still make the same choice as you did before, then I have nothing to say. I respect your choice."
When Elder Qu finished reading the documents left behind by Chen Meng'er, he was completely shocked. He was so shocked that he stood up straight from his seat.