Sally Oates herself is a simple woman from the town. Her presence alone would have not caused such a stir, however, it was her disease which made her, like the story says in a quasi satirical way
"raised her into a personage of much interest and importance among the neighbours"
Therefore, as much townsfolk with not much to be entertained with, the combination of having a very ill person and her claims that a mysterious man gave her a miracle cure to make her feel better must be surely a reason to exalt anyone for the smallest of reasons.
It was so good for them to have something new to talk about and someone at who to marvel, since in small towns those things are often part of the lore of the people.