Hi Rob,
Irfanview, Xnview... and the other image editors I tried don't display the embedded thumbnail. It must have been pushed around inside a bit too (by Picasa?) because the exif location for it has been slightly moved. I could hex-edit it (thumbnail) from the file and then view it okay with other programs. It looked to me like the thumbnail was actually created in your camera when you took the picture.
If you happen to have the unadulterated image from your camera for this image and want to send/post it somewhere I could tell for sure.
Some of us get our clues anyway we can, so yes indeed your images are well scrutinized :)