When commenting on a YouTube video, there is a checkbox where you decide whether to share that comment on Google+ as well [0]. Your choice is sticky - if you uncheck the box and make a comment, then that setting will be remembered and it will never post on Google+ unless you re-enable it. And you can choose whether you want to share that comment with the public or with particular people [1] (I can't think of any other commenting platform that lets you choose specifically who you want to share your comments with on a public page).
Where are you seeing which device you are using shared on Google+? The only place I've seen something like that is if you have someone you've accepted as a Hangouts chat buddy and you've opted into the "share which device I'm on" in the Hangouts settings (all that shows though is if you're on a tablet, phone, or desktop computer though, not specifically which device).
[0]: http://i.imgur.com/H9nHctO.png
[1]: http://i.imgur.com/YtnpjEb.png