Most likely, with the vents open, the charcoal burned at the rate allowed by that cooker, he probably just burned through the load he had in there. But, then, there would have been no coals. So...
my first thought, and that is that the coals were burning fine, hence the hot temperature, as Webers do not hold temps like an insulated cooker. But, the pork had dropped enough liquid, that the coals appeared black, but, where still burning. Two ways to check this theory, one is to flip the coals over with a stick, and see if there is still heat. Option Two, my favorite, is to think 'well, dagnabbit!' and reach in there with bare hands and grab a still burning coal. You can figure out how I know a black coal can still be lit from this point on.
