Why does race matter?

I'm reading an article on the Las Vegas shooting and the "journalist" threw this sentence in the end of the article...

Mojave had some 2,300 students last year, about evenly divided among blacks, whites and Hispanics, according to district materials.

That sentence appears after this sentence

"At this point, the indicators that we have found ... it's a dispute over a girlfriend," Gillespie told reporters.

What does this information have to do with the price of beans? As of this posting, there does not appear to be a racial component behind the attack. So why put it in? Because this is a fight over a girlfriend, we need a racial census on the school.

I guess I'm not a "journalist" so I'm not smart enough to figure it out.