I understand there are two methods of fire shining, one of which involves passing fire along the shoe itself once the wax is applied, and then the other as you describe: lighting the tin.The fire shine method actually refers to igniting flammable petroleum based shoe polish in the tin in order to liquify the wax, extinguishing the fire by starving it of oxygen with the lid, and subsequently applying the melted wax to the shoe while still hot. The liquid wax seeps into the leather pores instantly creating an even and smooth surface. Subsequent vigorous buffing with a cotton shammy will result in a mirror finish within seconds. It’s recommended this method only be applied in well ventilated areas given the risk of exposure to toxic fumes and one should always be mindful of the fire hazard it poses.
It’s a general misconception that leather should be directly exposed to fire when fire shining.
I often used this method personally during my attendance at a military academy. The results are mind boggling.
I've tried lighting the tin method and haven't gotten an especially good shine as a result of it. I get a lot better result from spit shining. From what I understand, it is a nice way to waterproof boots with wax by soaking the leather in the wax, but besides that, it doesn't seem especially that great.