I don't see why Why is our planet called Earth? is being considered off topic for this site. That it is about the history of a word doesn't make it off topic. Simply because there might be a better SE for it doesn't warrant its closure if it is still on topic (as per the FAQ) here. If that were so, all anime questions on SFF would be closed—they aren't.
FWIW, ELU would most likely close the question as being general reference. LinguisticsSE would spit on it in disdain.
If anything, the question should be migrated to ELU after consultation with one of their mods. Else, IMHO, it is a perfectly suitable resident for HSE.
I should also note that the question has 5 up votes to 4 down.