Got it. I got confused because googling suggests the English once called potatoes earth apples.
The Dutch word for Potato is 'aardappel', which literally translates as 'earth apple', AFAIK 'Erdapfel' is also used in some German dialects even though the official German word is 'Kartoffel' (derived the Italian word for a truffle), and of course the French use 'pomme de terre' ('earth apple'). Anyway it doesn't surprise me, that the English once also used 'earth apple' to refer to potatoes.
TBH naturally the first association I had, when reading earth apple, was the potato; is this an ATL were English uses the word earth apple instead of potato?
The common Dutch word for this crop is 'aardpeer', which means 'earth pear'; it needed to be distinguished from the 'aardappel'

. (Though 'topinamboer', 'jeruzalemartisjok' ('Jerusalem artichoke') and knolzonnebloem ('root sunflower' not 'sunflower root', which means something different), however the latter two are less common than 'topinamboer' or 'aardpeer').