Feng Xin was amazed at his deduction, as he didn’t know that Xie Lian had helped the boy chase away his bullies and had even chucked a fruit at him. “Li’l guy’s kinda smart, he actually figured it out.” Mu Qing, on the other hand, clearly suspected that something must have happened. He eyed Xie Lian.
It's like Xie Lian has two idiots on his shoulder. One is sincerely dense (Feng Xin), and the other is just socially inept (Mu Qing).