Is the story told in the Koran about the origin of Mohammed essentially true?

Yes, this was a true experiencing and divine inspiration when he had his personal awakening through an angelic messenger. So the inspiration was intentional and pre-planned for his life to be a great prophet and teacher. And his role was one of great challenge, for he as well was in the thick of things, in the very heart among the darkest of beings, and the many who were completely suppressed and subjugated by the interlopers, as well as many interlopers themselves who were genetic descendants of the Anunnaki, as well as the Reptilian shapeshifters who were among the human population enjoying their ability to manipulate people most directly. So he had many, many, dangers in spreading his truth, but he held his own for quite some time and has been a force for good for many, many people.