Those are just the "dead" thumbnails that don't get updated, and are smaller 96x96 pixel versions used for Explorer views. They'd already have to have been created or else you can't get anything programmatically.

These thumbnails are extracted from the files on request, as evidenced by the time involved and the need for video codecs. They tend to be 200x133 pixels, 200x112, etc. based on the aspect ratio of the video.