I'm fairly sure that is the origin of Erdäpfel. We certainly thought this was a funny name for potato when we learned French in Scotland :-)

When I learned German the word for potato was Kartoffel.

I suppose this "earth apple" formulation coming up in several languages is partly because potatoes are from the New World, and Old World languages won't have a "traditional" word for them. Whereas in English it's basically a loanword.

In Chinese one word for potato is "earth bean" 土豆 (the other word is "horse bell tuber" 马铃薯)

Polish is ziemniaki, where ziemia is earth.

Diverging but funny: "pommes de route" is a french-canadian colloquialism for horse droppings (on the street - "road apples")

french fries are pommes frites. the french term is also used in germany (though sometimes shortened to pommes or fritten).