Like all other sweeteners, it is untrue..... Since it has less than 5 calories per serving, they can say it has none. Same way with fat free milk, it has fat, just less than half a gram per serving, so they can say it is fat free.
It actually has 2 calories per teaspoon, and 96 calories per cup as compared to table sugar which has 15 calories per teaspoon and 720 calories per cup.
Sucrolose itself has no calories, but they need to put the dextrose and malto in there for a bulking and anti-caking agent. It is definitely the lesser of the two evils (sugar), but not completely calorie free.