This is neither HTML5 nor Flash
HTML5 capabilities of your browser are used to read this video, but this page doesn't include <video> tags. And doesn't even had one on the fly via javascript.
This page is a page and remains valid even when playing a clip.
But obviously, this has a cost: performance is less than using HTML5. And images may flicker...
The main purpose of this page is to proove that HTML5 is not what is seems to be and that we can still use xHtml and build modern websites anyway by using Progressive enhancement.
Free, open source and great Ogg/Theora codec for real browsers
H.264 codec for IE and other lamer browsers
Smaller size may flicker less (Ogg/theora version)
Smaller size may flicker less (H.264 version)