Frequently whites who turn up in poor black neighborhoods are there to do drug deals or are looking for prostitutes, which is obviously what the resident who reported him thought. The police often detain them long enough to get their ID because this discourages them from coming back and encouraging problem behavior in these neighborhoods, which the law abiding residents do not like. The residents often request this from “community policing” programs.
That said, Dylan acted in a very civilized, non-celeb manner. None of this “Do you know who I am?” from him!