No it doesn't. I'm saying it was justified, whether he was looking for a justification or not. The point is irrelevant, because she did, in fact, give him a justification.
If you're squaring off with some raging nigger, secretly hoping he gives you an excuse to shoot him, and then he pulls out a machete and charges you, that doesn't make your shooting unjustified. "Hoping" is not a crime.
As for Zack, I think he's motivated by contrarianism, anxiety over becoming the old guy who still defines himself by his 20's in the Marine Corps, and a longing for black dick. Those three motivations produce all sorts of crazy shit.