Just like Matt and his family, non actors asked to act just this once. People can shout down that opinion all they want but I saw absolutely nothing, nothing at all to convince me there is even a chance anything else is true. It was laughable at parts and I wanted to believe in what he was doing, I genuinely did but I couldn't go along with it, even half pretending with a straight face.
I thought the angle of that experiment was that he notices other people do nothing and then does nothing himself because they did nothing despite knowing that they have seen it. In that clip (I would have to see it again to be sure) it looked like the actors were not looking at the smoke or even gave any indication to Matt that they knew about it.
It looked to me like Matts decision was seeing the smoke, saw that noone else has noticed it, yet still says nothing, that to me is just odd. That's not following the crowd but choosing to ignore a potentially life threatening situation.
I would have to see it again though but I remember thinking they were all deep in their own thing and not giving Matt the indication they knew.
Maybe that wasn't even the experiment they were trying to recreate (I am thinking one about an American woman getting mugged I studied in uni), either way I didn't believe the scene like I normally do, to me it was in the script that he did nothing so he did nothing.