There's a good argument to be made that if Mormons are Christians so are Muslims. Both followed the same tradition, had their own new prophets, their own new revelations and holy books. Both revere Jesus. Muslims just deny his divinity. But there have been other Christian sects in the past who did that, as well.
This is a good quiz with a very nice looking map, but there's way too much time imo. Given that there are only a handful of major religions, it doesn't take long to guess all of them. The only one that might be a bit more obscure is Baha'i, but even then when you exhaust all the other options, Baha'i is something that logically makes sense. You could easily decrease the time to 1 minute and still have pretty high scores.
Do Mormons believe this?