The Closed Reality of Open World Games

As I was playing Saints Row The Third earlier, I was roaming around, unarmed, looking for collectibles. I walked down a little alley, with no notoriety, towards some sort of factory, and suddenly was taking fire from police. I found it odd, because nothing had been mentioned about restricted areas in the game, and, though I've gotten used to taking fire from rival gang members unprovoked, this was the first time the police had taken the initiative on such an occasion.