So what happened? Looks like his mixture went really rich or something, hence the black smoke. Like he wasn't getting enough spark. Then a backfire. Not really the end of the world, but would look scary. Right? Or was this something else?
he likely detonated his intake manifold. you can see a puff of smoke come out from the hood as well. i believe tahts why you don't spray under a certain RPM. he couldn't have been turning more than 3000 there.