Each full page is a giant image — there are actually two images for each page: one for landscape and one for portrait mode. Yes, I'm laughing on the inside too. There is no text or HTML, just one gigantic image. The "interactive" pieces where you can slide your finger to animate it are just a series of JPG files. When you press play on the audio file and see the progress meter animate? A series of PNG files.
The article then speculates that it was originally written in Adobe Flash and this may be a bad sign of what may come to the iPad due to Section 3.1.3 of Apple's licensing terms.