That looked reminiscent of some left over TNT. When size is of the essence (fit inside a backpack) you go with C4/SEMTEX. 25+ pounds of it will cause fatal internal injuries in a 100m radius. With the explosion emanating from that alcove 20 pounds would have obliterated everyone in that screen. I'm pretty sure they were shooting for body count and just are sub-par terrorists. Hard to imagine there are any dumb ones left.