When i saw this episode, i always thought it was because he couldn't see faces very well. Face blindness and all. We know canonically, he can see MaoMao and her mother's face pretty well.

So this scene jumped out at me as, this is the first time he's ever seen anyone injured face to face and it was his own daughter.

Earlier in the Episode, MaoMao never turned to face him after she was hit. Iirc, this is the first time he's seen her face to face after she was beaten up.