Sounds to me that he never actually uttered a racial slur but merely asked how they would feel if he had used that word he was hearing in the music. So apparently he is being relieved not because of using a racial slur at all, and some of the junior Marines, as they are being referred to, took offense at that. Perhaps he was trying to get them to see that the usage of the slur is wrong as it keeps reinforcing a negative about their race within themselves, and jeopardizing cohesiveness with the ranks.
yeah...that story reads funny. something is missing...I chased all the S&S articles related to it and there is no context.