"That....that's impossible, though." Elsa looks thoroughly confused, disregarding his statement of trust. No, this was even weirder.

"I've only been gone---for a week. Two, at most. Five hundred years is impossible."

She's looking back at her only companions, still confused, especially at what Chaos energy is, and just how that much time could've passed.

She's suddenly quite worried that she really is alone again, and she worries for Anna and her kingdom back home.