A lot of people do that. Sometimes, those sandwiches you see at stores only have food in the very front where you can see it. The rest of the sandwich has nothing in it. Lots of frozen pizza makers do this exact thing that you saw to save money and cut corners: they put all the toppings on one corner, and leave the rest of the pizza without so much as the sauce.
It's not just food, either. Some other companies that make shampoo and other hair products (as far as I know, only generic brands do this, not name brands) will make a big bottle to make you think you're buying more, but most of the actual capacity is dry as a bone. The actual product is contained in a small box or bag or something similar, which only takes up a third of the total space (half at most).
All of this counts as false advertising, which is actually illegal, and if someone decided to press charges, it could result in up to a $40,000 fine.
