It still isn't any of his business why his fried is being arrested. It is his business why he is being arrested if indeed he is arrested. It doesn't say in the story here that he was arrested, only that his friend was arrested. When you jump in demanding to know why your buddy is arrested, chances are you will get arrested as well and charged with hinder/delay/obstruct because you are interfering with the officers job. Sit back, shut up and listen when dealing with police. You may be right in the end but you will lose in the moment.