First instinct is to shake their head--but that's not...entirely wrong. They ran away from home, but there was nothing left at home. They ran away from nothing, literally, 'cause everyone needs something or they go crazy. Which they sorta did.

"I...left. I climbed a mountain, and monsters lived under it. Fell in."

They let their legs fly out from beneath them, crashing to sit on the floor. "You never found any of my papers. Or talked to my friends? Or other Frisks?" They're softly unsettled. Kuja's completely right; they know miles more than he does, and they never realized it before.