-Peacemaker-
.45 Cal
I am a Muslim and i will reply on this.
Your question is easily answered Mohammed(saws) himself taught it was a spirit/devil at first hand because in the time of Mohammed(saws) were he grew up Mecca (around pagans) they taught everything Super-natural had to do with Spirits or Devils so he assumed the same thing this is what he taught before. Now he went to hes wife and she assured them it was no devil, then Mohammed(saws) went to Christians to ask for the same thing but they assured him it was a Angel... See the Irony?
And i am pretty sure a devil wouldn't say that Jesus(p) is the messiah and one of the best messenger ever who lives, i am also sure a devil would not say that Marry(p) is the most righteous woman on earth even if the Jews were looking down on the arabs he still uphold the Jewish prophets in glory why??? Because he was commanded to say these things
Ps: I am willing to debate if mohammed(saws) is indeed prophesied in the new-testament
From a Christian perspective, salvation/forgiveness is found by believing Jesus is the Lord and submitting to him accordingly. The Devil would love to do anything possible to steer people away from that.