In plain English: "As a designated nuclear power we have the right to build as many warheads as we want and we are under no obligation to keep the world informed on its details". Technically, that rendition is correct. China does not have to disclose the details on its nuclear program to the US the UN or anybody. It is one of the perks of being one of the five designated nuclear states by the Nuclear Non-Proliferation Treaty.
Perhaps even more so than the US, China's neighbor Japan has had deep concerns over the secrecy of its nuclear program. Japan has taken notice to China's "increasingly bold" military practices and has become concerned that China is trying to eventually create an arsenal on par with that of the US and Russia, 10,000 warheads (I dont even think China has that much Uranium). Since the US and Russia signed the New START Treaty, which will cut both countries strategic stockpiles significantly, Japan fears China is taking the opportunity in America's stockpile reduction to build up its own. In fact it has gotten to the point where Japan is so worried, they're actually asking America to build up their nuclear strike capabilities and delivery systems. When Japan is asking you to invest in nuclear weapons rather than eliminate them, you know they must be worried. Japan wants America to stay powerful in the region to deter China from doing "something stupid" in regards to its nuclear weapons.
China has repetitively stated that its nuclear program is purely defensive in nature and even points to its no first use policy. However, most nuclear experts believe that promise to be complete bullcrap.
In the meantime, why not simulate your impending doom with this neat nuclear fallout simulator.