No, he wasn't.
Here's what's happening to Jahi's brain right now. There is no brain activity whatsoever. None. It is not getting blood circulation. The cells are breaking down. Her brain is decomposing. Soon it will turn into a liquid and flow out of her nose.
She is not coming back to life.
Read the book.
Women in Quebec and Australia have also recovered after being declared brain dead. The criteria do not seem to be infallible.
And if brain tissue actually flowed out the nose, bacteria from the nose would colonize the brain, and the patient would be all the way dead in short order.