Watch the video in the link. Once the Humvee passes, he's gone. If he's not in the Humvee itself, they used it to provide cover while they moved him behind their lines or somewhere else off-camera.
The guy is in central booking now, but it's just a weird tactic to try and handle it off-camera like that. Certainly not something that screams trust and transparency.
I watched this happen live. He was being arrested because he was out an hour past curfew, and he was taunting the police walking up and down a row of them by himself. He was taken away in the Humvee, but it did seem as though law enforcement attempted to use it as cover from the media cameras just in case the arrest went badly (i.e., in case they injured the guy).
You can look online and find all kinds of incarceration statistics and how they relate to race. They will tell you that roughly two times as many African American people are incarcerated than White people in America. That is a pretty huge discrepancy considering African Americans make up only 13% of the American population and whites make up about 60%. We are also the biggest incarceraters in the western world. We jail people at a far greater rate than do European countries.