Dave,
What happens if you select only one photo and then edit? If LR still shows all images in the folder, I'd suspect it to be a problem with LR.
Another test you could do is to select one photo, right-click on it, choose Reveal in Windows Explorer. A Windows Explorer window will come forward with the image selected. Drag and drop it onto LR. Does it show only the single image or the whole folder's worth of images?
-Kirk