Nunchuck chains or rope (on a toy?) are rarely long enough to wrap around anyone's neck. As you said, why couldn't they have just been unwrapped? I wonder if he hit his windpipe really hard or something.
There's the possibility. Some are made with longer chains/cords.
I'm guessing that he tried to bring them around his neck from one hand to the other too fast and didn't catch the other stick. It may have slammed into his head or cut off the circulation to his brain (if the chain/cord was long enough to encircle the throat area), and he passed out. I've had some get wrapped around my palm and the wood ends (holding the connecting material) would lock together briefly.
Too bad for one so young, too.
Bruce Lee with (I think) nine-inch nunchaku in, "The Return of the Dragon."