Hepzibah tells Jaffrey he's dreaming. Why?

Clifford told Jasper the house possesed hidden wealth. Hepzibah tells him he's dreaming.

"It is as certain as that I stand here!" said Judge Pyncheon, striking his gold-headed cane on the floor, and at the same time stamping his foot, as if to express his conviction the more forcibly by the whole emphasis of his substantial person. "Clifford told me so himself!"

"No, no!" exclaimed Hepzibah incredulously. "You are dreaming, Cousin Jaffrey."