It seems that members of minority groups are prejudiced against other minority groups, and since they don't suffer from the famous "white guilt," they don't restrain themselves from saying so.
There's also, if you read the post, an instance of a genuinely bigoted white teacher, and the fact that he hasn't been fired shows how powerful the teachers unions are.
Let's say a Taiwanese teacher of Chinese shouts in front of God and everyone "I hate Chinese," and proceeds to denounce the majority of our Chinese-speaking students as shiftless commies. Let’s say she treats them as such and manages to stay in the system until retirement.
Maybe a teacher posts on the board an offer to write college recommendations for 50 bucks a pop. Let's say that teacher is from Spain and regularly tells Dominican and South American kids they are ignorant and don't know their native languages. Let's say further this teacher makes disparaging remarks about their parentage, of a most unpleasant and vulgar variety.