The prison guards did use their brains; the torture chamber where Chief Historian Zuo and the Jia Brothers were held wasn't particularly close, so they couldn't hear or see each other's situation.
Chief Historian Zuo, Wen Qiming, had somewhat disheveled hair and seemed to lack strength, but it seemed he had no visible injuries.
Clearly, the prison guards were somewhat hesitant when handling him, naturally holding back a bit.
When he saw Zhu Yu and Lu Qing, he vaguely recalled seeing them the previous day at the Jia Residence, right next to Zhu Cheng. Upon further thought, it seemed they were also present earlier when Zhu Cheng had approached him in the East Wing to discuss matters privately.
They must be Zhu Cheng's confidants.
