Kosovo is part of Serbia.
Aside from that, those Russians are swine. Never, never, never trust the Russians! What they are saying is that is Serbia loses Kosovo, they will take it out on peoples who have nothing to do with the matter. It is all typical Russian bullying, and even when they act friendly, they are probably just drunk, and will forget it when they sober up.
Putin stinks.
Russia has always used Serbia as a bargaining chip against the West. It's obvious that they're using her again for their own ends. They couldn't care less about Serbia's territorial integrity.