It wasn't Chu Liang's fault.
His first reaction when hearing this was, there were clearly three undercover members, yet they mentioned only one; could it be that the other two were arranged by them?
Upon rethinking, he realized this was impossible, as Luo Yao and Pu Shan both had distinct lineage and identity, hence, impersonation was highly unlikely. The only explanation would be that the Earth Slaying Envoy had only discovered one mole, hence, making such a statement.
"There is a traitor among us."
"Right now, I am communicating with the two of you privately. The moment I make a move, you two must immediately attack 'Sixty'. I fear she may have a way to contact the outside, so we must kill her instantly."
The Earth Slaying Envoy said so.
Only then did Chu Liang understand. He must have been near Luo Yao just now and had some contact with 'Sixty' before, so he knew that his approach was not like that.
Therefore, he concluded that this 'Sixty' was fake.
