Even though the condiments say 0/0/0, there are often "trace Calories" or "trace carbs," which means they are there, but not enough to have to record on a nutrition label. It also means that if you have more than the serving size, those "trace" nutrients are no longer trace amounts.
But... I would assume you're not going to down half a bottle in 1 sitting, so it may not make a difference. Enjoy your Thousand Island.... and try out the "Big Mac in a Bowl" recipe.