Um… yes, actually. They are. The term “Hamburger”, in German, refers to someone or something that is of/from the city of Hamburg, which is how the sandwich we so love got its name. Similarly, people from Frankfurt are called Frankfurters, and people from Wien (the German name for Vienna, Austria) are called Wieners. People from Berlin are called Berliners… which became sort of the original version of this joke, I guess ;)
Philosoraptor, you are drunk.