JOEL - I think the teacher probably did not present the information exactly as his instruction manual intended it to be. Unfortunately our church is not completely void of people who still tend to demonstrate racist attitudes. The Church and gospel are true, but there are some people in the church who are not.
According to black LDS member Darius Gray, president of the Genesis Group:
"There is racism in the world. There is racism in the United States. Is there racism in the church? Yes, because we are a cross-section of the United States, of the people here. Now, is the Church of Jesus Christ of Latter-day Saints racist? No, never has been. But some of those people within the church have those tendencies. You have to separate the two." (See http://www.kued.org/productions/voices/interviews/gray.htm)

It would be helpful to have a chat with that teacher, and those who were offended, and the Bishop of the ward, to clear up any false teachings or missunderstandings which may have occured.
According to what past church leaders have said, it is not "wrong" to marry outside your race; it is simply not advisable to do so. The General Authorities of the LDS Church do not condemn inter-racial marriage. However, they have taught that successful marriage is most likely to occur when the participants are of the same racial background generally, and of somewhat the same economic and social and educational background.
Here is what LDS Church President, Spencer W. Kimball taught:
"Now, the brethren feel that it is not the wisest thing to cross racial lines in dating and marrying. There is no condemnation. We have had some of our fine young people who have crossed the lines. We hope they will be very happy, but experience of the brethren through a hundred years has proved to us that marriage is a very difficult thing under any circumstances and the difficulty increases in interrace marriages. A couple has not committed sin if an Indian boy and a white girl are married, or vice versa. It isn't a transgression like the transgressions of which many are guilty. But it is not expedient. Marriage statistics and our general experience convince us that marriage is not easy. It is difficult when all factors are favorable. The divorces increase constantly, even where the spouses have the same general background of race, religion, finances, education, and otherwise. We are unanimous, all of the Brethren, in feeling and recommending that Indians marry Indians, and Mexicans marry Mexicans; the Chinese marry Chinese and the Japanese marry Japanese; that the Caucasians marry the Caucasians, and the Arabs marry Arabs."

As you can see, the Church does not condemn inter-race marriage, they just want to make sure that a marriage is successful and is not jeopardized by differences in cultural backgrounds. Any couple, whether same-race or mixed-race, may enter the temples of the LDS Church and be married for time and eternity, as long as they are both worthy of such a blessing. Admission is not based on "the color of their skin, but by the content of their character."(MLKJr.)