Confused after Ep 1 - can big brother talk?

I thought I understood what I was watching in Ep. 1. Younger son who can talk & hear, older son who is deaf like both parents. But then who is the guy in the ice cream parlor who crushes on the girl with the cello? He was definitely speaking to her.

What am I missing? is it a dream that the older brother is having, that he can talk?