"Christian" means "follower of Christ." A Mormon couldn't be called a Christian since the Book of Mormon, authored by a single man, is their principal text. In fact, Mormons reject all Bibles except the one edited by Joseph Smith.
Plenty of Mormons act "Christ like", but they aren't followers of Christ per se.
I know plenty of Catholics whom I consider to be brothers and sisters in Christ, who believe Jesus is Lord and Savior and that we are saved only by his grace.
We tend to want to pigeon hole everyone into a category. I might be a member of a Catholic church not because I am a fan of their governance, rosary beads, or infant baptism, but because the particular church may well be a loving, supportive family of Christ followers.
I attend a Church of Christ, but I don't agree with everything in the church. Yet it is a loving body of earnest Christ followers who have been of tremendous support for me and my family.
C.S. Lewis addressed this perfectly in Mere Christianity:
"It (Christianity) is more like a hall out of which doors open into several rooms. If I can bring anyone into that hall, I have done what I attempted. But it is in the rooms, not the hall, that there are fires and chairs and meals. The hall is a place to wait in, a place from which to try the various doors, not a place to live in. For that purpose the worst of the rooms (whichever that may be) is, I think preferable. It is true that some people may find they have to wait in the hall for a considerable time, while others feel certain almost at once which door they must knock at. I do not know why there is this difference, but I am sure God keeps no one waiting unless He sees that it is good for him to wait. When you do get into the room you will find that the long wait has done some kind of good which you would not have had otherwise. But you must regard it as waiting, not as camping. You must keep on praying for light: and, of course, even in the hall, you must begin trying to obey the rules which are common to the whole house. And above all you must be asking which door is the true one; not which pleases you best by its paint and paneling.
In plain language, the question should never be: "Do I like that kind of service?" but "Are these doctrines true: Is holiness here? Does my conscience move me towards this? Is my reluctance to knock at this door due to my pride, or my mere taste, or my personal dislike of this particular door-keeper?"
When you have reached your own room, be kind to those who have chosen different doors and to those who are still in the hall. If they are wrong they need your prayers all the more; and if they are your enemies, then you are under orders to pray for them. This is one of the rules common to the whole house."
