Moli asked Li Yueshan if he had seen his brother. But in fact, she already had the answer.
Li Yueshan looked at her with silence; he didn't want to say anything else. He didn't want to make it sound like he was trying to exculpate himself. He had done something wrong, and he intended to take on the consequences.
As he stayed quiet, Moli didn't ask more questions. She already had the answers to the questions she wanted to ask. She had also figured out the reason why he did what he did.
So, she looked at him and said, "I guess you don't believe in the power of our base. That's why you did what they asked, right?"
He could have told Wu Chengyue about it and used the power of Sea City Base to rescue his little brother. In that case, he wouldn't have to betray his base under threat.