It makes perfect sense. When Kendrick is talking shyt on Control, he doesnt literally mean what he says. It's just friendly competition. The fact you took it serious is funny, like wrestling fans who think the wrestler actually hate each other in real life.
Of course he doesn't literally mean he wants to murder Drake, as in kill him as a human being, dumbass, but the intent behind it ("I want to break you guys down and be the undisputed king of rap") is absolutely real and you're naive to think otherwise.