A little more description of the cops actions would be interesting.
It sounds like they were responding to a dispatched call. Four cars 35 minutes after the rifle was put away certainly doesn't sound like an urgent call for service. Were their lights activated as the pulled up? Did they hold either of you at gun point? Was anyone placed in handcuffs or the back of a transport vehicle? Once the police had determined that you were no threat, what was their demeanor? Did you get a lecture from any of the officers? How long did the entire interaction with the police last?
Discretion is a valuable skill, however, open display of a firearm, especially an unloaded firearm is not a crime. The police have an obligation to respond and investigate, but we should be careful about giving into the hysteria of the moment.
Be safe.