What you saw in the video is just the explosives the guy used to kill himself. It started a fire in the truck which set off a larger explosive in the back consisting of TNT, RDX, mortar shells, artillery shells, and aluminium powder.
Al-Qaeda, TTP behind Marriott blast: Malik
*"The explosives expert in this committee, however, has submitted his report within 16 hours and on the basis of his past experience he has disclosed that the explosive material was high quality RDX and TNT. Earlier, in most of the cases potassium chloride, made of the fertiliser, was used. But this explosive material is of military type.
“We have recovered splinters of mortar shells and artillery rounds as well. There was one additional item seen this time and that was aluminium powder. It accelerates fire when it is mixed with the explosive material. So when these shells blew out and hit the Marriott Hotel it became a chemical that spread the fire fast and could not be extinguished,” the Adviser on Interior said.*
So unless you know better than an explosives expert (who was able to account for the fire), why would you think it is fishy?
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Although the events of this weekend were terrible indeed, I hope that it will inspire the government to exact a terrible vengeance on those who carried it out; those who ally with them; those who shelter them; those who give them food and drink; and all those who support them in any way at all.