http://www.liveleak.com/view?i=12b_1344268701
I'm no expert, but it seems right before the explosion, someone threw an explosive device out of the apc, and that device exploded - taking the vehicle too.
thoughts?
what ever it was, it was already very hot as it left the vehicle (notice its black color, in 00:02),
so I guess it was not a bomb that went off after it left the vehicle, but something that was already cooked inside and thrown(?) out of the vehicle half a second before it exploded.