Washing Griddle before first use
Whatever harm there was is done, so not much to do about it now, other than finally wash the thing before the next use.

New products often have either traces of materials from the manufacturing process, or a preservative coating for the time they spend between being made and being purchased; which is not generally something you'd want to consume. 

Whatever you cooked might have had some non-food grade oils, factory dust, or the like added by the time it was done cooking.