If it was all rehearsed with all the spectators knowing what was happening it was a fake - the key thing about any kind of flash mob thing is to surprise and entertain real people.

If it wasn't a fake, and real bystanders were involved it was pretty risky and genuinely shocking. Wouldn't you feel you had to intervene if you saw ambulance staff dropping a patient?

Here's the kind of thing flash mobs ought to be about.