“How Police Normally Responds To 911 Calls”

Friend of mine called police to report someone driving dangerously on a highway. Couple days later he got a call from unknown number claiming it is the police and they asked his home address so that they can some documents to fill in.

Is this regular procedure? Will he have to be a witness in the court?

if the person was driving dangerously and they were stopped police would need a witness statement from your friend. Typically the police would drive to the person's house or have them come to the detachment/station to provide a written statement. Having said that, if the friend is not from the area of where it was reported, the police might call by phone and do an interview over the phone or maybe send something by email. To clarify it was infact the police, just call the detachment/station to confirm you were contacted by an officer.