The fact that there's a correlation between OBEs in healthy individuals and certain neuroelectrical anomalies doesn't per se prove or suggest OBEs are hallucinations. Such conclusion is based on the assumption that "the mind" is a product of the brain. But that's not the only viable model or approach to studying consciousness. More and more scientists (including neuroscientists, like Dr. Hennacy Powell) are finding certain peculiar correlations that suggest the need to revise that model, and consider the brain as a receptor of the mind. Don't stop at the book reviews and endorsements and read her book 'The ESP Enigma: The Scientific Case for Psychic Phenomena'. Very insightful.
Having said that, the fact that OBEs might be an actual phenomena or human ability doesn't exclude the possibility of the brain going haywire and producing hallucinations. Still, my point is there's enough research and evidence out there to suggest OBEs are not mere hallucinations (for instance, cases in which individuals accessed information that was out of physical reach).