Others have given great answers, but the short-answer is that it's not a "disinformation campaign," nor is it organized. It's because Lemmy has a lot of leftists, especially Marxist-Leninists, and MLs both support AES ("Actually Existing Socialism"), like the PRC, and critically support capitalist countries forced into allying with them against the Global North's imperialism.
In terms of their net impacts on the world, the US and EU far outweigh the evils of Russia. Russia is certainly flawed, but unlike the US and EU Russia doesn't rely on expropriating vast amounts of wealth from the Global South, sanctioning, couping, or genociding those who go against imperialism. It isn't because Russia is some moral paragon, but because they simply lack the means to be imperialist, they are boxxed in by the west and lack the financial capital to rely on expropriation of wealth.
As for the PRC, it gets far more support, because it's the leading socialist country. 800 million people were lifted from poverty, and it's rapidly improving. Even when the west runs propaganda against them, like the COVID lab leak theory or the Chinese spy balloon hysteria, the PRC is being widely supported by the Global South as the PRC is providing a genuine alternative to the genocidal west.
If you (or anyone else) want an introduction to Marxism-Leninism, here's my Read Theory, Darn It! introductory reading guide!