There are no beliefs, metaphysical or otherwise, behind atheism. Atheism is lack of belief.
Atheism is a lack of belief
in a god or gods. There are metaphysical implications in such a stance. Read up on metaphysical naturalism if you get a chance.
The worldview of people influence their actions, including political actions.
Exactly correct!

How much influence is at play here is the question I am raising.
The Chinese Communist Party does not define atheism. They might define some "Sino-atheism" just as they define some "Sino-religiousness".
If they were
real atheists rather than just sino-atheists, in what way would they act differently?
What do you mean by 'atheism', here? Real atheism, which is simply the position that no gods exist, or some ideological position that will let a totalitarian government include religions as their enemies?
The latter, obviously, as per observations of what is going on in China.
Of course they are not. They are acting as people of power who don't want to share their power with some gods they consider non-existent. This is a trait of people who don't respect the worldview of others, it is not a trait of atheism.
Again, not my point. Let me hopefully steel-man the conversation:
A political group, declared atheists, gain power. They believe that religions are false because there are no god or gods, and they believe that religions are a danger to social well-being. So they decide to limit and then probably remove religions in they can.
They are
acting on the idea that they regard religions as a danger to society rather than to some pure idea of atheism.
I think we are all on the same page at this point.
People then think that I am arguing that "they are doing this because they are atheists!" But I am not arguing that. I'm asking how the metaphysical beliefs behind atheism -- the idea that the universe is all there is -- influences their
actions. I see the statement that it is "atheism vs theism", "science vs superstition" and "materialism vs idealism" as an indication of thought processes behind their
actions, which is ultimately about control.
The fact that we see the same atrocious behaviour in other governments with state-sponsored atheism is possibly significant. It's a bit like how some pro-Communists in the West defend Communism. You point out to them how communist governments lead to totalitarian governments and they will say "Oh, that's not REAL Communism! Real communism just means the people own the means of production. We've never had real communism, only people who just wanted to exert totalitarian control!" But that just ignores the connection between communism and the development of totalitarian impulses.
So that's the point I am making: what is connection between the metaphysical beliefs behind atheism and what is happening in China? Is there a connection? I think there is. I'm not saying "they are doing awful things only because they are atheists", but rather "they are doing awful things, and atheism is one aspect of the reasons behind it." The idea that all officially-declared atheist governments behave that way suggests some kind of connection.