I think the DA will have a lot of trouble making these charges stick, as the law they were indicted under requires you to show that the group engages in criminal street gang activity. What actually happened was a political protest that turned into an altercation. The police, at the end of that video, are indeed explaining that some of what is being shouted constitute threats under state law. However, the target of that explanation is not among the protest group -- it's the family that took issue with them that is being warned to stop making threats.
To me it sounds like a bunch of rednecks engaging in protected free political speech, combined with emotional overreactions on both sides when the conflict started. Bad behavior was clearly rampant on more than one side of the conflict. Apparently the government has decided to take sides rather than impartially referee the dispute. They put charges of terrorism and gang activity before the Grand Jury, and the Grand Jury bought it. I'll be very surprised if the trial jury does.