Unless business hours for the lot are posted then it's private property but open to the public and unless the police observe a crime going on then they have no justifiable cause for a Terry stop. Sitting on a curb in plain sight is not going to stand up as justifiable cause under Terry.
The guys who were beat up will shortly become wealthier.
The business hours for the business, and thus the owned lot, would be the same in many jurisdictions. I don't know the law where this incident took place, but around here if the place is closed for business then that means all parts of the property are now closed to the public.
Around here it would be a justified Terry stop as loitering even on business property after business hours is a trespassing misdemeanor offense. If you have no business being there then the cops may just stop by to figure that out. Most of the reason for such laws is to stop tagging and after hour vandalism as well as prevent potential break ins.
It was clear in the video there were open nearby businesses the two guys could have waited at for their ride to arrive across the street. Lights on and everything. Instead they chose to sit on a curb inside of a private parking lot for their right in the dark. Most cops will investigate that and that is a good thing for them to do. If the asshats hadn't been up for trying to get a good youtube video they would have apologized for being there, stated their ignorance of the matter, and asked to leave freely. Of which it would have been done more than likely. They instead started by stating no the officer and questioning her authority for the stop in the first place. I'll tell you that such actions do not tend to go well when interacting with police.
Does that mean I support the remainder of the police actions which the back up arrived? No. I thought they were unprofessional as hell. Does that mean what was done was wrong legally speaking? Nope. This is a piss poor video to use as justification for bad police actions over all though.
Actually just checked the FL law on it.
Section 856.021(1)
It is unlawful for any person to loiter or prowl in a place, at a time or in a manner not usual for law-abiding individuals, under circumstances that warrant a justifiable and reasonable alarm or immediate concern for the safety of persons or property in the vicinity.
While they were in fact not actually breaking the loitering law, that doesn't mean a cop doesn't have the legal right to stop them for that since they are arising suspicion by being in a dark parking lot by themselves of a closed business. That isn't enough to arrest them on legally speaking, but it is enough for a Terry stop to determine if there is something more to the initial suspicion that may lead the officer to believe there is an immediate concern for property or safety.
That's the loitering law, still looking at the trespassing one. Not that it matters since the one I already mentioned gives the officer legal justification for a Terry stop in that scenario.