No, it doesn't. You show someone he's out of his depth by attacking his argument, not by pointing out that the counter-argument comes from someone famous. Are you seriously claiming that no one you've never heard of can possibly argue against a point made by someone you've heard of? That's a sheepish mindset.
The fact that Rob Pike wrote a usable language that is not OOP in the sense that the commenter thinks of OOP, in which you have composition without inheritance is direct evidence against the commenter's point of view that to do composition you need to be doing OOP.
However sometimes it does make sense to appeal to authority, if only to let someone know how far out of their depth they are.