There is just so much stuff in this fight.. I mean, the King represents ultimate Nen power and Netero couldn't really harm him with regular attacks - and all this time we are believing that the Ant King is the strongest being on earth; a monster that can't feel pain or can't be harmed.
There are so many animes where characters with uber strength can't be damaged by anything and we have been conditioned to believe this fact by dozens of other mangas and shounen stories when the reality is that humans already created technology capable of wiping out entire landscapes in mere milliseconds. All this time the Ant King thought this was a one-vs-one fight with fists and power, that he can rule the world with his incredible physical strength; a illusion he unconsciously created for himself since he doesn't know anything of the world or humans and how far these have already advanced. There is a much bigger power than physical strength, and it was created by humans themselves.
Netero always respected the power of the King, but the fight was already decided from the beginning. He knew that there is something more dangerous than Nen or martial arts, and keeps looking down at the Ant King; to him, that King is nothing more than a mere peasant, a little child with no real knowledge.
That short moment of fear that the Ant King felt was a wake-up call: there is something worse and more cruel than Chimera Ants, and that's humanity.
And the fact that the bomb used was being called 'Rose' and used by 'dictators of small countries' was the almost best thing in the entire episode to me; that message in this information is just soooo huge, I could write another paragraph about it
Togashi is a amazing guy