IS THIS RACIST? Please, people of all races, answer!?

I go to a private high school where the majority of the student body is white, as is the faculty and Dean of Students. Today, we got to dress up in costumes according to the theme our advisors (homeroom teachers) picked. My friend's (call her K) advisory (homeroom) were dressed up as dead musicians. K dressed up as Ray Charles and another (M) as Louis Armstrong (Both black musicians). They put on black makeup to make them look black. Each advisor got to make a skit about their costume and perform it in front of the students. When K's advisory performed, the Dean called her and M to the office and made them take off their costumes because she thought it would be offensive to the [mainly white] student body. It got into this whole ordeal, and it ended both students having their parents called and M being sent home. All of the black students (theirs only 6) came to the Dean's office to tell her that she was being racist by not letting a white person dress as a black one. Is this racist?