This isn't a bad thing, or a good thing, it's just a geopolitical reality.
Serbia is still within even a weakened Russia's sphere of influence, and is unlikely to move towards Europe.
But with Russia not looking so great, they still need geopolitical allies to invest and help grow their economy, possibly help with security i.e. technology.
China actually helped Serbian nationalists during their Kosovo genocide, and got their embassy in Belgrade bombed because of that. Well, because they let the Serbs use a part of it as a signals and comms center. Point is, they have very recent historical ties.
Also, Russia isn't in a position to really push back on China for anything, so, here we are.