Christ existed before he was born, and he appeared to people in the Old Testament.<quoted text>
How did some of the people in the Book of Mormon get called "Christian" before there was a Christ?
See John chapter 1
"In the beginning was the Word, and the Word was with God, and the Word was God." verse 14 "And the Word was made flesh, and dwelt among us...."
Christ is the word of God, he existed before he was born.
I know I am preaching to the choir here because you are a well educated Christian...but:
The whole purpose of the Law of Moses was to point people to Christ. From creation's dawn to the meridian of time and throughout all eternity the plan was for Jesus Christ to save us from death and hell. All of God's children rely on the Atonement of Christ, both before and after the meridian of time. Christ's atonement is infinite. The people before Christ's coming looked for the signs of his coming and awaited the salvation he would bring with great anticipation. Undoubtedly these people had faith in Christ, and under that assumption, I think they could qualify as Christians.