He was lucky it didn't ignite the vapors above the puddle.
ignition temperature is about 495° F (232(232° C), temperature of a cigarette heater is 1100F. 1600 after a 2 second drag.
You have your chemistry totally wrong as well. Gas fumes don't require any percentage of O2 to ignite, all they require is the presence of O2. It will use whatever is present until it's gone. I think what you are getting at, is gas needs to be at a certain density to ignite as a chain reaction.
Doesn't really matter anyway, since it is illegal to
vape in non smoking areas