[Giller]

From some sciency website:

"...gasoline vapour has a much lower autoignition temperature than the gasoline itself. Namely, if you spill gasoline on a hot road (say in the hot summer day) you will be able to ignite gasoline by contact with a cigarette easily, just because of the gasoline vapour layer that would be produced above the surface of the gasoline. Not to even mention throwing the cigarette into the container with gasoline that has been closed for some time and is therefore full of gasoline vapours."

I remember Myth Busters doing tests on this. It's next to impossible, but given the right set of circumstances, it can happen. That's of course assuming it was a cigarette issue, which I'm not sure is even in evidence.