It means that people will base their beliefs in credibility on signals they receive when they are not in a position to judge credibility themselves.
In your case, you don't know the science, you simply trust that this Rhodes Scholar does. So, that's a shallow metric.
I doubt very much that you go to your mechanic to diagnose your cardiovascular health just because he had a heart attack. That would also be a shallow metric. A deep quality metric would be visiting a cardiologist.
Rex Murphy doesn't have any tacit knowledge of climate science, he has opinions. He doesn't know science, he doesn't practice science, but he's still going to confidently proclaim the scientists are wrong. Oh, but he's a Rhodes Scholar, who studied...well he didn't actually receive a degree from Oxford!
Shallow.