I have no idea where that narrative came from. But it was repeated here.☺
Is that what happened? I dunno.
For every parade I’ve been to, it’s not just the parade route that is blocked off, but nearby streets as well. There are signs, barriers, police cars, etc. all stationed several streets over in all directions from the actual route itself. The police cars have their blue lights activated and some officers are directing traffic. I just have a hard time seeing this happening as an accident. The person would have noticed that he was entering a parade way before he actually encountered the marchers.