Wait.... pro-Ivanka? What were pro-Ivanka people doing to get an arrest threat?
Being there. Now if they had been anarchists burning buildings, burning cars, breaking windows, and beating the hell out of passers by, no such threat of arrest would have been made. In fact, the police would have protected the anarchist as they had their fun.
The mall parking lot is private property and the mall can dictate what actions occur there. Just like they can set their own curfew inside the mall for teenagers.