What could have started the false reports concerning the young marquis and the handsome shepherdess?
Clearly Rose's own hallucination.

She had seen the marquis somewhere, without having been seen by him; she had fallen in love with him, and had partly lost her reason and imagined all the rest, she thought.
"And so you have never even looked upon the beauty of that dream ?" she said, with a smile.
"Never even looked upon her," assented the marquis.
"Then I do, in downright earnest, beg your pardon for my dream," said Salome, gravely.
"But I have already given you absolution, my erring daughter?
_Benedicite! Benedicite!_" replied the marquis still laughing.
At that moment there was a light rap at the library door, followed by the entrance of a footman who placed a small, twisted note in the hands of Miss Levison.

She opened it and read: "MY DEAR CHILD: It is after ten o'clock.

We go to church at eleven.

Sir Lemuel has not yet rung his bell.