Propane is a hydrocarbon, so burning it will create carbon dioxide, and hydrogen oxide, that is water.
You may have increased the humidity in the garage to the point adding extra solvents from the paint remover created the fog some how.
I do not know what type of paint remover you are using, but i have two concerns. First your health. Are you sure you want to inhale the paint remover fumes?
The second, what is the paint remover doing to the fiberglass body parts? fiberglass is porous, and you may end up with paint remover under the paint, no matter how much to clean it after.