This one is a bit of a stretch. Current pipelines from Russia to China were running at capacity before the war. The new pipeline, the Power of Siberia, will be able to carry 1/6 to 1/4 of what they sold to Europe. And it wont be done for a couple of years. Theoretically, the chinese could buy more natural gas from Russia, but only after somebody spends a few billion on new pipelines, LNG plants, ports, and so on. At that point, maybe they could buy 1/2 of what the Russians were selling to Europe 2 years ago.
The russians have serious infrastructure issues before they could sell the gas they were selling to the Europeans, and in the interim some of those gas sites will get closed, and will cost a bunch to reopen.
Also, gas is market priced globally. Putin needs to sell as much as he possibly can at market rate. The only deal he can cut with Chinese is half roubles, half yuan. He wants dollars, bad, and he will sell his gas to anybody he can first.
Its much more complicated than you make it seem.