To some degree, I read that as a product of this being a transcript of a conversation. It's tough to capture a conversational setting in writing (even good written dialogue rarely makes for realistic spoken conversation). Also, Schmidt actively pursued setting this meeting up to talk with Assange directly, and based on a lot of the informal banter during the conversation, it definitely seemed like no one minded about being interrupted.
I was especially amused when Lisa Shields spilled water on her laptop, and Assange quickly 'saves' it from damage - somehow I was immediately reminded of the scene in Ronin when De Niro's character "accidentally" knocks a cup off a table, and Stellan Skarsgård's character instinctively catches it.