It is not wrong it was just not accepted.
Let's explain the circumstances. In German there are two words for these sweet things you eat to coffee or tea and somehow need a baking book to know how to make. First is "der Kuchen" which correspondes to "cake" in English and then there is "die Torte" which correspondes to "tarte" in English. There is no third word like "pie" in German. So a "Kuchen" is made with flour and baked. "Eine Torte" does not need to be baked and is quite creamy. It can have a baked bottom though. Now a pie is also baked and it normally has a filling. So if you have a filling of fruits you would call it "Obstkuchen" or "Früchtekuchen" in German which are certain kinds of "Kuchen". But if you fill it with something that is not sweet like meat it would not be a "Kuchen" anymore, because that has to be sweet. Such a savoury pie would be called "Pastete (fem.)" in German.
So "ein Apfelkuchen" is an "applepie". But a "meatpie" is "eine Fleischpastete".
I hope I could be of help.