Everyone present was stunned, never having expected such a turn of events. Jin Guangyao mournfully cried his wife's name again and again, a hand cupping her face. His eyes were wide, and his tears fell like rain onto her cheeks. Lan Xichen said, "A-Yao, Madam Jin, she... I'm so sorry." Jin Guangyao looked up. "Er-ge, what is going on? Why would A-Su suddenly kill herself? And why would you all suddenly gather before Fragrance Palace to make me open the secret chamber? Is there something you're not telling me?" Jiang Cheng, who had arrived late to this impromptu gathering, said coldly, "Zewu-jun, please provide an explanation. We are all in the dark as well."
I don't think we're ever given a plot-driven explanation for why Jiang Cheng was late here, and I'm unclear if there's some kind of character note we're supposed to be taking from it (I personally like to imagine he heard a commotion going on outside his window, was like "Ugh, I bet Wei Wuxian is stirring up some drama again. Can't believe I have to deal with this again after 13 years," and shoved his pillow over his head, before remembering Jin Ling might be getting into trouble and getting up with a heavy sigh).
But there's something kind of darkly hilarious about the idea of him showing up late to find Qin Su bleeding out on the floor, Jin Guangyao sobbing over her dead body, and half the cultivation world standing around yelling accusations at each other. I just picture him bursting in there like that one Community meme gif:
