At this point, my theory is that he reached down and lit the damn thing on fire and it flared (orange propellant flash was visible on TV NEWS) burning him, then detonated as he fled.
Here's 2 photos.
PHOTO #1 = Daily Mail shows man in black hoodie (fits description of black hooded man who approached a checkpoint, then broke eye contact) running away at speed, not acting like the other spectators.
PHOTO #2 = I've outlined in YELLOW this pair. One man wears PUFFY GRAY coat (seems over-bundled-up compared to other spectators), while his partner in ALL BLACK bends down, messing with some object on the ground that's about the size of a large tallish backpack. It's also located almost exactly where the blogger puts the "approx detonation point."
That pair outlined in YELLOW might be the "Friends of Obamatollah" we're looking for.