Earlier quoted context omitted.
I could be wrong, yes. But why impossible? Take this example: https://en.wikipedia.org/wiki/Zero-knowledge_proof#Discrete_... - all parties exchange are essentially random numbers (which doesn't count as "additional information"), yet they establish the fact that Peggy knows x . There's that footnote about how r must be truly random, of course, but as long as everything's done right there is no additional information…
Any information exchange must go through a medium and it's not possible to create one with zero metadata.
I suppose the fact that it's Peggy and Victor who are running that protocol is simply irrelevant. They're talking about that value of x after all, and nothing related to that topic is revealed beyond the proof of the fact that Peggy knows it. If she'd appear in person, wherever she wears a red shirt or a white one would be might be considered "information" but it would be completely out of scope.