It's called reasonable grounds to believe a crime, or in this case, a violation of the law occurred. The 911 call to the police, with an accompanying address and details describing the violation suggests those criteria were met.
“The 911 call to the police, with an accompanying address and details describing the violation suggests those criteria were met.”
Did they get BOTH sides of the story first? Or just act in behalf of the businesses interests only?
We do not know the circumstances at the time of the argument between P and D. If P left promptly after warned to leave, no criminal trespass. If P did not leave and continued make a scene and arguing, etc., P is guilty of criminal trespass at that time.