He looks at her, checking that reaction. She comes from a flat world, with no "day" or "night", but it has ordinary weather patterns? Perhaps... her world is an ordinary planet, and it's a lack of technology- no cars, no phones, what else don't they have?- that makes her think otherwise, and she's merely accepting Earth's roundness as another bizarre quirk of this dimension.

That's probably it.

He points. "Rain. Kweengow has rain?"