No, it means the label is not accurate.

If they say they have 9 grams of fat, but it's actually 9.8 according to the USDA, then you have 0.8 gram of fat not accounted for, and that's about 7 calories.

The Hidden carbs calculator gives you the worst possible scenario, if the manufacturer is hiding or rounding something (fat, carbs, calories or protein) the calculator will assume all hidden things are carbohydrates. This is the best/safest assumption, since there is no way to figure what part of the label is erronious.

Wa'il