I believe fix-a-flat constains some flammable chemicals (propane, butane), tire changers don't like it for that reason.
But even heating just compressed air in that scenario is Darwin Award material. And this sounds like it might have been a two-piece wheel, dangerous in itself.
I thought they changed the formula due to that. It's illegal to use Fix-A-Flat in many states and all federal government vehicles because of the explosive potential.