Nothing illegal about hanging with friends in front of a closed store. Nothing illegal about finding and wearing a backpack. Surely people are free to walk away and not talk to the police.
Must have been an unconstitutional random stop by some cop who was profiling poor minorities.
Those that won't get it, don't get it.
"To spit on your hands and lower the pike; to stand fast over the body of Leonidas the King; to be rear guard at Kunu-Ri; to stand and be still to the Birkenhead Drill; these are not rational acts. They are often merely necessary." Pournelle