Why is it sped up?
Because he ain’t no Bruce Lee.
Nunchucks are super cool, but as a weapon you have to ask yourself, is this better than a good stick?
With the amount of expertise this guy has, absolutely.
He can feint or switch up the precise target of an attack on the fly, in a way that probably will not be visibly telegraphed to anyone who is not also this talented with nunchakku.
In video game terms: imagine fighting an opponent who easily and frequently move cancels, but the time between the cancelled move and the new move hitting you is 50ms or less.
Also, as a nunchakku is smaller, lighter and gets the benefits of leverage (from bending at the chain), it takes less physical exertion to hit as, or nearly as hard as a stick or staff.
It does have less range, but again, with this level of skill, he’s likely able to lock up and possibly disarm a stick / staff wielder.