Email from an employee is also a plausible mechanism for how that idea might have come to him in a dream. Information not fully processed and turned over when awake can turn into clear ideas in dreams. By committing himself to get rich in the stock market when awake, he primes himself to think about related information when he sleeps. It could be that he never even consciously connected the two and believed it to be a premonition.

Or it could be as you say. No way for us to know.