And yes you do, or at least a clearheaded, rational person would need more evidence.
One incident of bad behavior by a group of kids does not make them kids who must be put in a special school. If these kids have been general troublemakers and have other serious incidents of bad behavior, then the punishment probably fits. But if this is the only incident, the punishment is definitely too severe.
And a suspension from school is not a vacation for any kid who plans to make passing grades and eventually graduate from high school. They have to stay caught up with their class. And, do you know what sort of students these kids are? Do you know anything about them other than this one incident? Oh, yeah, that's all you need to know about a group of middle school kids.
Did you watch the video? These kids weren't little angels who decided one day to just say "Hey, let's insult, denigrate, threaten, demean, put our hands on and disrespect an old lady today until she cries." They were practiced. They were bold enough to do it, record it, AND post the recording. That's bad enough...but she was also an authority figure. Those kids were bold enough to insult, denigrate, threaten, demean, put their hands on and disrespect a person who was in a position of authority over them. How well she represented that authority is irrelevant.
If they had punched her in the face would you make the same argument that this could have been the first time they punched someone in the face so they should not be severely punished?