I think it's actually just a red herring. I think one could better define "private" in this context to mean "between two individuals", with the false implicatio

I think it's actually just a red herring. I think one could better define "private" in this context to mean "between two individuals", with the false implication that they mean "away from advertisers". Facebook has proven itself an exception to Hanlon's Razor by this point, so I'd say its probably deliberate.