It's not that sparks inside your car can ignite a fire, but rather that if you get back into your car and then back out, you can build up a static charge on your body, which could then spark when you touch the gas nozzle and ignite any available fumes
I guess, basically, that is what I meant. I have experienced that very thing - luckily I was not about to put gas in when I felt the static charge. It's amazing how we have survived for so long in ignorance of this dangerous task we do day in and day out. If we still did have full service gas attendents, perhaps the chances of this ever happening to us would be nil. Before, the days of self-serve one did not hear about such horrific accidents at the gas pump.