As with Paul, Ammon makes and equivalence between God and the pagan deity. It is quite certain that most people would not have understood either the Greek god nor the Lamanite god in the same terms as the God preached to them, but the important aspect that Ammon is teaching is that God is at the same place in the conceptual universe. For Ammon, it is probable that King Lamoni was a polytheist, and that this Great Spirit was the deity considered to be the highest ranking of the multiple gods.
King Lamoni says that he does not "know the heavens." This must be seen as a comment on Ammon's religious terminology, not our understanding of "the heavens" as the study of the night sky. Where we might thing of astronomy as a study of "the heavens," it appears that Ammon has some conception of heaven as a multiple, or layered place. Thus he asks not simply about "heaven" where God resides, but "the heavens" in plural.