'The Love-sick Maid text is given above and indeed predates Burns. There is no indication that he was a highwayman, and the description given in it implies that he was a jockey. You'd need to compare all of the versions to see which derive from the Burns adaptation. It's likely Scottish versions derive from Burns. As in many ballads, particularly Irish, the song is about the difference in the status of the jockey and the rich girl. It doesn't make it clear but perhaps the jockey is a Catholic and she is Protestant. John Moulden might have a better idea.