The Pyro's homemade flamethrower does not actually work. By accident, the device has become a sort of totem, channeling the Pyro's latent pyrokinetic ability to create flame by thought. It is a psychological crutch, a way to rationalize a freakish talent, to use it without feeling guilt. The Pyro could conceivably shoot fire from a vacuum cleaner or a waterhose or the Pyro's bare hands, but the Pyro does not. If the flamethrower burns them, it is not because of IT, the thing far back in that shattered little mind, that which gives the flame, killing and destroying because, if the fire really comes from the inside and not the gun, that would be VERY BAD, that would be admitting the past

and so the Pyro hides behind the mask and the flamethrower, trying to retain control of a born talent, a prodigy who's skill has grown out of grasp.