I have painted several cars at home, have used a MR. Heater propane heater, torpedo heaters and gas pilot light heaters. A long time ago I painted a 57 chev and then realized the gas pilot light thru the fog of clear coat, and thanked God I did not blow up.
Many years later, I tought my Sons to paint at home, told them to be sure and turn off the heater during the spraying. One of my sons said he had expermented and sprayed right into an open flame and the paint did not ignite. Still we use common sence and turn off the heaters. but we still have the fans going, so it would seam were still at risk. I have no answer why , but I should have blown up and did not. Like you said,myth busters needs to do this.