If it is vitiligo, it isn't dangerous. I don't know if it always progresses or if it might just stay the way it is.
If doesn't look like the pictures I've seen of vitiligo, but it doesn't look like the pictures I've seen of illnesses either.
Keep taking pictures every week and see how it changes. Maybe how it changes (or doesn't change) will give people a clue.
If he seems healthy otherwise, just continue to take good care of him and try not to worry. If he has any other symptoms, then post them too.