It does seem possible that something which greatly alters a person's brain chemistry to the extent that a stroke does could indeed alter that person's sexual orientation. There have been many cases of people recovering from strokes who have developed entirely new skill sets and/or personalities, so I see no reason why the same couldn't be true of their sexuality. Granted it's probably extremely rare, but it still seems plausible.
I notice a lot of people in here reacting very negatively to the idea. I think that's more a reaction to the notion of somebody "turning gay" because it sounds way too close to "choosing to be gay", which we all know is an annoying and ridiculous myth. It's important to note, however, that this is not a claim that somebody decided to turn gay, but rather it's a confirmation of the fact that some essential element of brain function dictates sexual orientation in a way that's totally beyond human control.
The Gaian Gay-Straight Alliance
Our goal is to spread awareness of, lessen unwarranted hatred of, and create a safe haven for the LGBTQ community and their allies.