If so, how are they not the preaching the truth?

The answer to the question is, "No. It is not Christian." Like all non-Christian cults, the Jehovah's Witness' organization distorts the essential doctrines of Christianity. It denies the deity of Christ, His physical resurrection, and salvation by grace.  These make it non-Christian.  In addition, to support its erring doctrines, the Watchtower organization (which is the author and teacher of all official Jehovah's Witness' theology) has altered the Bible to make it agree with its changing and non-Christian teachings.Typical with cults that use the Bible to support its position is a host of interpretive errors:

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The Jehovah's Witnesses are discouraged from looking into Jehovah's Witness' history or old Watchtower literature which is replete with contradictions, altered doctrines, and false prophecies. Instead, they are indoctrinated repeatedly against basic Christian doctrines (Trinity, deity of Christ, etc.,) and into the notion that they alone are the true servants of God and that all others are either in "Christendom" or simply unbelievers.

Primarily, the Jehovah's Witness' organization is a mind-control organization that uses its people to pass out literature and send in "donations" to the headquarters in Brooklyn, New York.

Thus the Bible is an organizational book and belongs to the Christian congregation as an organization and not to individuals, regardless of how sincerely they may believe that they can interpret the Bible."(The Watchtower, Oct. 1, 1967, p. 587.

Conclusion

The Watchtower organization of the Jehovah's Witnesses is a non-Christian organization that uses its people to promulgate false doctrines, collects "contributions" for distribution of a multitudinous amount of literature, and expands its grip into the lives of its members and their families.

It is a non-Christian cult.