Earlier quoted context omitted.
It's using existing mechanisms in YouTube's JSON API to find suggestions and play them. All the true "magic" is provided by YouTube's engineers. Not to take it away from someone who writes the right lines of JavaScript at the right time, but you don't have to place the guy on a pedestal. The real lesson here is for yourself and others here who think like you -- if you tell yourself that things like this take superhum…
Nothing is more enjoyable than seeing posts on the internet by programmers who look at an idea, then scoff at its simplicity while making a list of all the idea's component parts, pointing out how easy each component is.
(Of course, everyone thinking that this is even remotely the same thing as Google Instant is also completely missing the real innovations in that product.)