Placing a flame on any chlorinated solvent, Freon, chlorine gas, or even Halon will create phosgene gas. Never breath the white smoke. This guy is very lucky that he is alive although he will probably never be the same.
As for welding on galvanized metal, that is a different animal. It is metal poisoning. Symptoms of that can be reduced by drinking a lot of milk. To avoid breathing these vapors, use a strong fan for ventilation and a welding mask respirator.
Just like the guy said, household products can be very dangerous especially when exposed to an open flame (or TIG/MIG/ARC). I agree with his method of using a solvent to remove gunk but you really have to make sure all of the solvent volatilizes and is gone before welding. Also, to be really safe, you should purge any fuel tank with Nitrogen gas to remove any Oxygen before and while welding or you could go KA-BOOM!!!