Unless Muslims believe in Jesus as deity (and salvation through Christ's atonement) as Mormons do, that seems an unlikely statement.

Mormons do get drawn outside of Christianity by some christians for a variety of reasons (non-trinitarian, open canon, cosmological background quasi-polytheism), and some people have suggested classifying the faith as another Abrahamic one as a means of sidestepping that discussion, which may be where one could get the idea that the comparison to Muslims is a good one. But if Mormons are outside mainstream Christianity, it's only marginally so.

The point I was making is that both Islam and Mormonism are based on Christianity and so share many common beliefs, but they both extend on this base. Personally I find Mormonism a fascinating religion, but I do think it has moved past being just another branch of Christianity.

No. Muslims believe only parts of the Christian bible are divine. Mormons believe all parts of both the old and the new testament are divine, and addition believe in a third book (that I've only read the intro to) which has additional tales of Jesus Christ and companions.

They are as Christian as catholics are, perhaps even more so as in my opinion they follow his ideology a whole lot better.