According to Strong’s Concordance we see the book of Acts is the first place the term “Christian” is used in print (Acts 11:26 is the earliest record). It would stand to reason the followers of Jesus were using the term to identify themselves. Mormons are taught that no one truly followed Jesus Christ after His death, therefore eliminating the need for this term of Christianity or Christian, and the need for a restoration.
“See CHRIST, CHRISTIANITY. On the false assumption that Christianity had its beginning with our Lord’s mortal ministry, his birth was chosen to mark the beginning of the so-called Christian Era.” Bruce R. McConkie, MormonDoctrine, 131.