No. Yes. I don’t know.
I have a lot of respect for high school teachers, I work with them on occasion, it is a hard and often thankless job and one of the hardest parts of their job is maintaining order. During the regular term there are a few tools that teachers have for disruptive behavior, such as sending students down to the principal’s office, detention or threats of detention, and so on. Such tools were not available in this situation. This student did not offer much alternative, it was his way or nothing. I know that many people like to think of teachers as petty autocrats, and this is a common stereotype in high school movies, but I think it is mainly not true, and people who think that teachers are often or even frequently on a power trip are mistakenly using the worldview of some past version of themselves. In this situation I am inclined to think that the teachers were trying to do what they thought was best for the day, and the student was being difficult, and the reason I am inclined to think this is that in my experience most teachers try to do what they think is best, and many 18-year-olds like to test the limits of their power.
The teachers in this case had to make a decision in real time, and I don’t know if calling in the cops was the best decision but I’m not sure I could have come up with a better alternative on the spot.
It is not a question that makes sense, he was ejected for refusing to remove his kente, I do not think a white student would wear one. I suspect that had another student worn something they viewed as violating the dress code, and they asked him to remove it, and the student did not comply, the reaction would have been the same, though in the absence of an example we will not know.
I think it is a big leap to accuse these teachers of being racist. Perhaps they are, as most Americans (and everyone else) are racist to some degree, but I think as a group teachers tend to be less racist than the average person, even less so in districts like this where people of several ethnicities live side-by-side in relative harmony. A much simpler explanation is simply one of a student testing his power against some teachers during a school function, and the teachers responding to that test of power the only way they could think of on the spot.
While the yarmulke is not a good example (it fits under the regalia, moreover just wearing the mortarboard alone is headwear and therefore a religiously acceptable substitute), Sikh headwear as you pictured is an excellent example of something that schools will certainly have to learn to accommodate. Perhaps that is true of the kente as well, if a student’s culture requires it to be worn daily.