"surely exposure to Muslim adventurers is possible... though unlikely?"
There also appears to be commonality with Judeo-Christian belief, to a much greater degree than Muslim, but the three, Judaism, Christianity and Islam, do have common early origins. Plus, there are aspects showing some commonality with the Egyptians as well. Also, one of the names for this "god" was Votan, which might seem to throw a pre-Christian, Northern European influence into the mix (Wotan).
It's very tempting to say that these beliefs did not arise completely independently of one another, but I just don't see any practicable way to explain such a thing.
The explanation can be found in the Book of Mormon.