Well crap I didn't know that....I just open my tailgate and slide the can on top and fill it up and shove it back in. Better change my ways.Mythbusters did an episode on that too. They concluded the answer is no. Im sure a malfunctioning cell phone or battery could do it.
Static electricity can start a fire in specific conditions.
You should always put your gas can on the ground when filling them up especially if you have a bedliner that insulates.