Diegetic sound

Sound that comes from the world depicted in the film

Diegetic sounds is things like voices of characters and sounds made by objects in the story. 
Here quite simply it is used to display a conversation between two character this scene is important on 3 elements it introduce us to some of the main character in the series ,it helps build a back story and understanding to what the audeince has seen and also it is the first time these main characters meet and it is core to how the character devlop with each other.