He is inferring that Mormonism is not Christianity.
Well it isn't. Sorry.
I don't really know what the litmus test for being considered a Christian is, but Mormonism does disagree with several major central ideas to the Christian Faith....For example,
So, under what category of faith, parallel to Christianity, Islam, Judaism, Buddhism, Hindusim, etc., would Mormons fit under?
Seems like they themselves call themselves Christian, go to Church, and praise Jesus, it takes a pretty high ground to accuse them of not being Christian at all.