Also, you should know that there is a long history, which continues to right this second, of racism within law enforcement,. This is not really conjecture of our part. it’s a pretty well-established historical and current fact of life in the US. See for example on the role of race in the modern prison system, which you can read about in this book:
So, while the individual who called the police on an 18 year old for wearing cloth to a graduation ceremony might not have had a racist motive in his/her actions or imagined their actions in such a way, there is a very long history of police being used to “control” the social behavior of black Americans. Black Americans, especially young black men (and especially those of working class status), are treated far harsher for far less in the American criminal justice system. Again, these are not flights of fancy, these are pretty well established facts of life here in America.