When a prophet has spoken in the name of Jehovah but that event has not happened or taken place it was not Jehovah who spoke. The prophet spoke it presumptuously. Deut 18:22.

[2] And even the foretellings of events which did take place may have been made by evil people and worshippers of another god, as stated in the same book,

If a prophet or the dreamer of a dream arises in the midst of you, and gives you a sign or else a wonder, and the sign or wonder he has told you comes to pass, and he says, Let us go after other gods which you have not known, and let us serve them; you shall not obey the words of that prophet or the dreamer of that dream; for Jehovah your God is testing you. Deut 13: 1-3.

From these words it is evident that the actual foretelling originated in the Divine but the incitement to worship other gods in the proprium of the prophet, who was allowed to make such a suggestion to people so that they could be tested, as is stated. This among other reasons is also why on many occasions in former times people who worshipped the baals and other gods even prophesied, saw visions, and dreamed dreams, and also why what they uttered actually happened, so that they frequently led others astray. These people are referred to in Jeremiah 23. And besides these there were others called diviners, soothsayers, sorcerers, familiar spirits, among those who applied themselves to natural magic, from which nothing at all Divine could be foretold, only what was contrary to the Divine, that is, to the Lord, and contrary to the good of love and to the truth of faith in Him. This is magic, no matter what it looks like in outward appearance.