Exactly. The 3 black guys were, at that point, just walking around. We know now that they were up to no good, but the attacker couldn't have known that for sure.
We don't know what words were exchanged, or if the three black youths were armed.
We are just assuming he didn't. Did he see them jiggling car handles? We don't know. Why do we think he didn't? Just because he is white? Oh, he's white, he must have attacked them for NO reason unlike the reasonable black folks who never engage in violence without probable cause.
Come on guys, use your heads for something other than a hat rack.
You can't try to steal a car by simply standing around ... you have to, well, I dunno ... engaging in activity that would effectuate the theft of a car. Maybe someone witnessed it. The chances were great that someone witnessed it. They were black, not invisible.