Your premise is that China had already achieved socialism and then went backwards towards capitalism but in reality they were a semi-feudal semi-colonized agrarian state, had a communist revolution, and began building towards socialism which is a process that takes generations. If socialism comes after capitalism and capitalism comes after feudalism, it means that with China being a feudal pre-industrial society during their revolution, they must enter into and move through a capitalist phase to develop and expand the means of production and socialize labor in order to create the conditions to build socialism. Socialism can not be built directly out of feudalism, just like capitalism couldn't come directly out of slave economies.

The key is that the entire capitalist phase of China was controlled by a Communist party with the express goal of building socialism, unlike every capitalist nation without a dictatorship of the proletariat, where the express goal was to build capitalism in order to make money for the capitalists. It should be obvious at this point if you look at the metrics: Chinese people have a higher quality of life, more purchasing power, greater social welfare, and virtually none of the key social problems that the capitalist core countries have, despite the capitalist countries having vastly more developed economies earlier and vastly more resources readily available through colonial plunder and chattel slavery. China is very clearly run by true Communists because if not, they wouldn't have any of these things, and would look more like India or any other nation in the Global South.