It's nice that she gets down on their level. A lot of Monsters were taller then Frisk - Asgore comes to mind - and while it wasn't a problem to look up to talk to people, it's nice to look at someone eye to eye.

"Not that long." It hadn't been that long since they RESET last, so Frisk assumes whatever went down happened during that time. So no, not that long but time is an illusion for them most days. Who knows how long their adventures in the Underground actually lasted for.

"Um, where is this place?" Probably for the best to start here, they think.