Very interesting but how is it done?

This is really interesting.
I am wondering how is this done. The image are being loaded but the flash swf is ready. The images when loaded they have a white border around their thumbnails version and if you click on the thumbnail with the white border around the image is displayed immidiately.

But if the border is gray and you click on the image thumbnail the image holder tells you that the image is now being loaded.

ie how can the swf be still loading but available for interactivity :red:

http://www.airtightinteractive.com/photos/

thanks