No, racism is about the perpetuation of white supremacy. A black person can not engage in racism*** because they do not have the institutional power of white supremacy behind them. While Micah Johnson's actions were designed to attack a group of people beyond the ones he personally killed via fear and intimidation, these killings are not a part of a systematic violent oppression of whites because no such system exists.
The rebranding of anti-white rhetoric and violence by black radicals as "racism" is a right-wing tactic designed to dilute the meaning of the word. These killings were not hate crimes. They were not a part of a pattern of genocidal actions. They were 'just' murder. Perhaps terrorism.
***Johnson was no doubt prejudiced and discriminatory. But that's not the same as racism.
I don't know if it's laughable or scary that you think the way you do.