I just watched it, and I'm not sure what to think. I've heard of people (who I suppose are very socially conscious individuals,) under the impression that they were straight because that is the norm. People tend to soak up socially acceptable ideas/interests and then get to a point where they realize they were lying to themselves, and considering this person has experienced memory loss it's possible that he may have had moments of realization about his homosexuality and subsequent repression in his life that he has forgotten.
Despite what I know about the role genes and hormones play in sexuality I still say it's still possible he just woke up gay. There's no such thing as a gay brain anymore than there is a such thing as an alcoholic brain. However there are such things as brains that show signs of what causes these individual traits. As the researchers who tested this man pointed out, the hormones and genes that push someone in the direction of a homosexual preference show their signs in other areas cross the entire brain. That doesn't mean the whole brain has to be changed, just the part that connects the pleasure center of the brain to thoughts of the opposite sex/ or same sex. That may just be one small area of the brain, and strokes affect individual parts of the brain in strange ways all the time.