"said to me with a sort of a smile, which usually ariseth from pity to the ignorant..."
See in text (Part III - Chapter X)
Though Gulliver is unfamiliar with this country, he requests to stay permanently immediately upon hearing that some of the inhabitants are immortal. That the Luggnaggian man smiles in a way that suggests Gulliver is “ignorant” is Swift's way of foreshadowing. Gulliver seems a bit too eager to stay, and this country seems a bit too good to be true.