It's just a back-formation. The language pretends that the latter part of a word is a productive suffix and makes new words by appending it to other roots giving new meanings. For example, hamburger is a German loan word which in that language is an indeclinable adjective of provenance, meaning 'something or someone from Hamburg'. (It's actually formed from a real productive suffix -er appended to the place name). Many such place names in Germany have their adjectives subverted to indicate a food or drink, as the American president did when he announced "ich bin ein Berliner" ('I am a small pink boiled sausage').
I digress. A Hamburger was applied to denote a beef pattie in a roll as typically made in that city. When the Yanks got hold of it they decided that "-burger" was a productive prefix (which as far as German was concerned was bollocks) and gave us cheeseburger, chicken burger, and so on. The irony is that McDonalds now sell things with these names in Germany which can now indeed also make back formations with -burger, like Schnitzelburger. There is of course no such place as Schnitzelburg.
I once saw an American tourist ask in a tourist office if he could visit "Cheeseburg".