...that Their Calorie Counts May Be Wrong

That's because in order to make sure you're getting at least as much as you pay for, the FDA is more likely to penalize a food manufacturer for overstating the net weight of a product than understating it.

As a result, manufacturers often either "generously" package more food than the stated net weight or make servings heavier than the stated serving size weight.
 
Try this with an ordinary food scale, put some products to the test by checking the actual net weight and serving size weight.  Sure enough, you will find that a number of popular products are heavier than the package says! And that means you may be eating more a lot more calories than you think.

It really is best to avoid "foods" in a box as much as possible.  Rather go with foods that are fresh and local.