[blueskin_]

>It could be a genuine robbery, or a piece of improv street theatre, or a sociology experiment.

If so, irresponsible experiment/theatre, and they have only themselves to blame if someone did get tripped/punched/rugby tackled/hit with martial arts moves/arrested. The fact that nobody did any of those is the main problem - if someone did, many people would have felt more confident too, both at not being caught up in police issues around it, but also via a safety in numbers instinct.