Calculating carbs at a restaurant is always difficult. The food comes to you all dressed and pretty, the carbs intermingling with the fats and proteins. The apparent quantity skewed by the size of the fancy plate. Sugars hiding in the dressings and marinades. And don't forget about the bread you downed before your meal came. Or that spoonful you stole off your table mate's plate. And you should always consider the Q factor (aka the quantity factor--the more fats and proteins you cram into your stomach the longer those carbs take to digest, causing you to miss that key moment when your insulin and glucose digestion are supposed to peak at the same time).
Calculating at restaurants is difficult.
But having a paper table cloth an a crayon make it a little easier.