It was funny as heck!
Sounds like a Rube Goldberg way to get the same result at considerable more cost in the propane/cold beer ratio. I am a strong believer in the KISS priviple of engineering; Keep It Simple Stupid!
Whether he burned it or just blew it off, releasing propane from a tank will chill the tank. Becomes obvious when you run into a tank with a leaking valve that isn't discovered until the tank is filled and it won't completely shut off. Best remedy on small tanks not worth pumping down is take out back and open her up, vapor out. As the pressure in the vessel reduces, the liquid remaining rapidly chills. Usually takes a third to half of the content before the remaing liquid is chilled to 44 below, the boiling point. Then we can remove and repair or replace the valve without fighting 200 PSI pressure. Repair and top it off, the frost line immediately vanishes. Why use up half a tank to get a less efficient cooling than my using about a gallon of liquid straight on the cans?