Can Enamled Cast Iron cause fires? I heard of someone who supposedly had a fire while cooking on an enameled cast iron grill pan. I am not sure if this was due to negligence on the part of the chef or if there was something in the grill pan that could have caused this. What do you think?

Could some materials like the enamel coating have reacted to certain foods?
Metal (cast iron) would have to melt before it would burn, and it takes a lot of firepower to melt metal-- that's why we cook in it.  Enamel likewise isn't going to burst into flame at temperatures generated on the average stove or grill.  Something smeared or coating it might, though.

Like grease.  On a grill pan, what you describe sounds like a grease fire.  Possibly (but not necessarily, could have just been clumsiness or an accident) caused by negligence of the chef, the drippings from whatever was being cooked in the pan caught fire.  If you leave grease/oil in a hot enough pan long enough, its certainly possible for it to catch flame, especially if there's something with a lower smoke point floating in it.

That said, plain cast iron does react with acidic foods, but in a way that makes your food taste off, not burst into flames.