User blog:Lifebleedin/how does killua know zenos ability

how does killua know zenos ability dragon dive? normal people cannot see nen, they can only see conjured items from conjurers. killua never knew about nen when he was a kid so its impossible for zeno to show killua his ability in his childhood. the only way killua could have seen his ability was from the gap in G.I where killua went back to take the hunter exam but he came back immediately after he got his licenses so this is high unlikely. therefore there is no way killua would have known that zeno was part of the invasion. is this a plot hole or am i missing something