I agree that in the context of what's going on worldwide, China is doing much better for sustainability than the rest of the world. So, in a sense, criticism is invalid because it would be better directed at the countries with higher emissions per capita, as you say. Criticism doesn't exist in a vacuum and we should steer clear of anticommunism and sinophobia.
On the other hand, there's no way China should keep its level of industrial growth and usage of fossil fuels indefinitely in the face of world threatening climate change. I think it's a fair criticism to make when trying to assess how future socialism should look. In other words, China may be doing very well for itself by keeping per capita emissions very low relative to the rest of the world, but even still, it burns amounts of fossil fuels that are fundamentally at odds with trying to prevent climate collapse. Is that mostly due to Western capital? Yeah, pretty much.