Translation:No, it does not come here, but it flies here.
Does "idejön" have a more specific meaning in this sentence than the generic "to come", i.e. to move from somewhere else to where the speaker is? If it is flying here it is surely coming here as well.
This offered two choices for correct translations, the one above, and also, "No, he does not come here, but it flies here."
Why are there two different pronouns in the second suggestion? If he/she/it is flying here, then isn't he/she/it by definition coming here?
You are right, I don't think that other translation should be acceptable. In the sentence "Nem idejön, hanem iderepül" both actions have the same subject.
But to get any sense in this sentence two different subjects are necessary?
No, HE does not come here, but SHE flies here. Person a does not come, but Person b comes, by plane. Works also with two males, or whatever. But the important part is imho that we are talking about two different subjects.
Might even work in a dialog:
A: Is Adam coming? And what about Steve? He usually flies, doesn't he?
B: No, he does not come here, but he flies here.
Still confusing, but otherwise it sounds like total nonsense.
What is the contrast suggested by 'hanem'? Surely, flying is a way of coming, too! Does 'jön' imply walking? (I wouldn't think so..)
Moreover, the 'but' in the English translation is not very natural. To my ears & eyes it's more natural to just repeat the subject (it/he/she) and leave out the 'but'.