I can tell you there is no 100% verifiable scientific proof to either prove or disprove that gasoline can be ignited by a lit cigarette.
There are to many variables that can affect the results.
If more detailed information was avaliable on your actual situation, an answer may be possible.
An example on the variables:
A match held above gasoline will ignite the vapor and cause the gasoline to burn.
If a breeze keeps the vapors from accumulating the match will have no effect.
The match put directly into the gasoline will be extingushed by the gasoline.
The fire marshal is correct. A cigarette will not light gasoline.
Throw a lit match in a can of gasoline and the gasoline will put the match out.
Do not hold the match over the can of gasoline since it will ignite the vapor and cause a fire or explosion.
A cigarette can and will ignite the vapor, if the conditions are wright.
"When the cigarette was was smashed into his left shoulder and the sparks "rained" down to his belly area" this is all it would talk to ignite the gasoline fumes. When the sparks "rained" down they hot hotter due to the extra air they were exposed to. This was all that was needed to ignite the gasoline vapor and start the fire.
Any time air is supplied to a smoldering object, it will get hotter and burst into flame.
Example: Watch a Blacksmith, watch what happens to his coals when extra air is applied to the coals. Extra heat and fire.
Information on gasoline vapor below.
Injury caused by gasoline fires below.
Please read each link completely. Some are rather lengthy but all have information that will be helpful. Many are actual OSHA and other government publications.
If I can be of anymore help just ask.