Good observation. I’m a structural engineer and it’s staggering to consider the force it took to bend that barrier with pressure.
Where is the black bag on the right of the street light in front of the lead runner on the side walk in the first photo?
I’m not saying this was in any way the device but it is missing from the second photo?
The force of a half dozen people, violently thrown and/or falling against both barriers would seem the only likely way to bend it like that. If it was a pressure wave alone, I would think that the chairs behind as well as the mailbox would have been more disrupted, all having much greater surface area. I just don't think it likely that the force could have come from in front of that barrier.
Those poor people.