For those who expect Luffy's reward to be 5 billion, 6 billion
he seems to laugh at those who predicted Luffy to get 5-6B bounty.
either they predicted much higher-> which means the WG wants to keep it low so they can cover up the threat he could cause.
or they predicted it too low which means the WG wants to let the people know he is too dangerous and the worst criminal.
it could go either way and it depends on the WG's strategy on dealing with Luffy.