The thumbnails are drawn directly from the catalogue itself and therefore show each picture in its adjusted state.
ListView's main purpose is showing metadata in a convenient list form, but it does have some basic metadata editing features. These will probably be developed further in the the future.
To edit a single picture's metadata
Click the thumbnail and a "File Info" style window will open, showing that picture and the metadata fields that are currently active. You can edit the values of most of IPTC fields, though not keywords.
To edit multiple pictures' metadata
ListView currently only allows you to edit one image at a time. To edit more than one, you'll have to return to the standard Lightroom interface.
One helpful feature is the column of tick boxes which works in conjunction with the two close buttons: