China is a big country. they announced bitcoin will return to zero whether this is just a prediction or they have valid data about bitcoin in the future will go to zero.
More like wishful thinking is what I say it is. They have no idea, they don't control the rest of the world or the internet at least yet.. Until than they can say all they want, it only works in their country.
But they can influence it to some extent since a lot of BTC miners were Chinese residents or owned by Chinese. Say if one day China considers making those guys fall into the line, to whatever plan they have for BTC. It would cause a huge disturbance in BTC.