If he's been doing this delivery route for years, he probably knows which people are going to give him trouble, so he probably knew that registered mail was going to trigger bad behavior and was prepared. Having a video recorder when having to deal with potentially hostile people is a good CYA move.
Plus, high-capacity recorders are cheap enough now that you can get one, let it run your whole shift, and just clear it at the end of the shift if nothing of note occurs.
Also a good idea to tape one to the dash of your car. Same rationale.