The author uses this passage to show that the King is unusual primarily through the line where he states, “So of course Nobody walks slower than you.” This suggests that the King thinks of "Nobody" as an actual individual, which is a play on words and a whimsical interpretation that is characteristic of the absurd logic found in the world of Lewis Carroll. This indicates a level of absurdity and a unique way of thinking that sets the King apart from conventional rulers. Therefore, the best option is:
He explains that the King thinks that Nobody is an actual person.