Lets start over from the beginning...
I went to research the joke in question. It is part of his monologue on an episode of SNL, where he's joking about how being black is the new white. Here is the line in question, and ill go back a few sentences to provide some context:
"The [NY] Nets moved to 'Brooklyn', how black is that? The courts black, Jay Z's the owner, a rapper, how black is that? He only owns this much of the team, but he acts like he owns ALL of NY, how black is that? I've got a movie coming out...Django Unchained, I play a slave...how black is that? And in the movie I have to wear chains...ummm...how whack is that? But don't be worried, because I get out the chains, I get free, I save my wife, and I kill ALL the white people in the movie...how GREAT is that? And how black is it....."
It's difficult to grasp the prosodic features, or the emphasis he puts on certain words, through type, so here's the video...
Jamie Foxx - Open Monologue - SNL [HQ] - YouTube
We can now see the context of the joke as it was told. The person doing the killing is his character, who he refers to as himself, or "I". The white people he refers to are specifically the white slave owners within the movie (with the exception of the white man who freed his character, whom he did not kill). Not anyone else.