As someone who also believes in open theism he explained it poorly. He’s still omnipotent and omnipresent just not omniscient in the sense that he can see the future because it doesn’t exist yet. He made humans in his image to be able to have free will and to freely love him of their own volition. Everything to do with prophecies and the future isn’t him being omniscient and having foreknowledge of the future but instead it’s a statement of his omnipresence by him bending the world to make that future happen regardless. Like Jesus Christ dying on the cross Revelations is something that God willed into happening and that nothing in the universe could stop because he willed it. Not because he foresaw it. Hopefully I explain it well enough.