Camera tricks often make small demonstrations appear large.
I think it will be exposed because many people now walk around with camera phones.
If you look at the 'crowd', it is only a couple of heads deep.
Signs are held to cover the area from that thin line to the wall in the back, giving the appearance that the space is full of people, except where there is no sign held up. Just going by the relative size of the heads of the people in the background, there is a lot of open space between the front row and the people over by the wall.
Note there aren't multiple layers of signs competing for the camera view. That's because there is no one back there to hold any up.
A close shot flattens the apparent depth of field, so the people in the background don't seem as distant. Once aware of what to look for, images like this one won't fly in the future.