I know very little about social media. My son knows a pretty fair amount. He has had a GMail address for 6 + years. He opened a Google+ account approx. 3 years ago but didnt start using it until one year ago. I just noticed that his YouTube subscriptions and videos he has commented on are available for anyone to see on his Google+ account, after clicking Profile and About. He tells me he didnt know these two things were linked like this, he thought a history of his  YouTube selections (subscriptions/commented on videos) were only viewable to him. Does it seem plausible to you that he could have been unaware of the connection?
How does the Google+YouTube integration work?
youtube;google plus