A gang implies that the group is involved in some sort of illegal activity like drug dealing/trafficking or extortion. The reality is, most of these clubs are made up of bored middle-aged men with a few younger guys in their 20's thrown in and even fewer guys in their 50's. They get matching clothes and ride around because they find it fun and, being in America, they carry around guns or knives because it makes them feel even more powerful when combined with the bike that they're on OR because there are real biker gangs out there that like to start shit when possible.

Besides getting into fights, sometimes speeding on their bike, or shooting up in their own time, these groups aren't actively (at least not yet) participating in any kind of illegal activity. Most of the people in these "gangs" hold jobs and have families.

For example, here is video of the horrible people that make up the Cossacks, one of the "gangs" shown in the pictures from incident. Video there's some more, too. Here's another one with shots of families and some decent homes of members. Do you think a guy with a nice home, some dogs, a family with children in their teens, and a stable relationship with his wife is going to join a biker gang and go around selling and transporting meth, extorting money from bar owners, holding up a gas station, etc...?

The reality is, one bad apple probably started off a chain reaction. This bad apple could have been a single person or an actual biker gang that partakes in illegal activities that decided to show up for biker night and start something.