Well actionscript is very similar to javascript, so If you can do one you can probably do the other. It is mostly scripting used to produce that effect. Check out a range of physics effects you can rip open and see how they work. http://www.flashkit.com/movies/Scripting/Physics/index.php I think it could be produced very quickly(although, im not a flash coder or actionscripter), And it probably took ages to get it as 'tidy' overall as the site is. There are LOTS of tiny details that would have taken along time + probably longer than the border). It can be hard to tell how long something takes in flash, depends alot on the designer and their skill level - the better they get the longer it takes usually.
* The flash source files are available here: http://www.neave.com/lab/ I take back what i said about 'quick' - I cant give an honest answer about that.