Theory #1: despite three decades of not being remotely racist, in fact affirmatively doing things a racist would never do like volunteer with underprivileged African-American youth and protest police treatment of an African-American homeless man, he spontaneously becomes profoundly racist one year in his mid-thirties, starts ignoring "suspicious"-acting people with pale skin even though he's called police on them in the past, and then hunts and kills a black young man for sport, after calling the cops so that they'd arrive right when he committed his premeditated racist murder.
Theory #2: He's called the police nearly fifty times on men and women, young and old, black and white. Sanford, Florida has a large African-American population. The last half-dozen suspicious person calls just happened to involve African-Americans. One of them vigorously attacks him, something he has never experienced in the past with his ~50 police calls, so he does something he's never done in the past, which is utilize his conceal-carry pistol in self-defense.
Now apply Occam's Razor.