I assumed that the weight of the hamburger was the entire sandwich, and not just the meat patty. (OP: 'hamburgers cost more than new cars' and not 'hamburger costs....'

Most sandwiches have at least a bun. Many come with lettuce, tomato, and condiments. Others have bacon, cheese, egg, peanut butter, avacado, onions, mushrooms, .... You get my drift. Besides, this was back-of-the-envelope and I don't think that arguing 1/2 pound versus 6.8665 ounces is reasonable. The statement seemed odd enough that I wanted to check it out