Originally Posted by FUNiOP
But really, I'm just more confused why it was thrown in at this particular moment.
Maybe Togashi was planning the next arc and suddenly he realised: "Oh, shit, Killua isn't a Hunter, he can't take part of this". And he solved it making Killua get his licence during Greed Island xD
I don't say more because it would be a spoiler of the next arc...