^Interesting... it says they shot it entirely in-camera. So either the fire and vapor were real and full-scale or there was some kind of forced-perspective illusion going on -- but in the latter case there would've needed to be some VFX for the interactive lighting on the ground beneath the flame.
It's possible this could be real; the main issue is that the cloud from the fire extinguisher seems improbably big. But then, it was shot at night and the cloud was brightly lit, so that might've made it seem bigger and more impressive than Adam's small-scale test in the daytime. And the fire stream here seems smaller than the one from Jamie's flamethrower. It's possible Jamie just overbuilt his.
Also, if it was real, then timing was an issue. It was edited to look like the flamethrower fired first, but in the long shots, compared to what the Mythbusters achieved, it looked to me like the extinguisher must've fired first and gotten up a good wall of CO2 to block the flame.
But there's still one reason to suspect VFX were used in the long shots, and that's safety. If this was a professionally produced music video instead of a bunch of idiots goofing around, then I doubt they would've permitted one person to fire a flamethrower directly toward another person with only a fire extinguisher as protection.