Maybe the condition for healing someone to this extent was that the person healed wouldn't remember who made the wish? Just a guess, but it would maybe explain why Morel told Leorio not to tell him about Killua healing him? I'm probably way off, though.
I know his appearance was short, but I hope Gon isn't completely his usual self. I want him to undergo some sort of change after his amazing development in Chimera Ant. Still, I"m excited to see if he meets Ging. I can see him just not talking to him, similar to something Luffy did in OP.