Can Enamled Cast Iron cause fires?
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.