The implication of Lamoni’s question about Ammon being sent from God was clearly that Ammon might still be at least a semidivine person, if not the Great Spirit. Thus, Ammon has to repeat that “I am a man.” What Ammon then does is link being a man to being a creation of Jehovah.
Next, Ammon introduces the concept of the Holy Spirit. He doesn’t give much information, except that the Ammon declares that the Spirit is not God, even though it is called “his Holy Spirit.” It was that Spirit that communicated with Ammon. Therefore, it was not Ammon who was sent from the presence of God, but rather it was “his Holy Spirit” that was sent to Ammon, who communicated with him according to God’s will.