Just to be clear, the parent (who is now deceased) was the one with the nudist behavior. The child, who is now 40 has some child like behavioiurs It wasn't a sudden change, I believe he was always like this , sort of arrested development. My question I guess was is this possibly a result of the parents nudist activities.

I comnpletely understand about nudist colonies and people enjoying the nudist lifestyle. In fact there are a couple nudist camps near here.
You are correct in that I could ask him about it, but we are not really close. Also, I don't feel I have a problem with it, just sort of interested in why. I really respect him in most ways, its just this behavour I don't understand. He did express interest in moving in with us and possibly having me be a father figure, That was a little disturbing to me for some reason.