He knew a lot of pieces of information. He spent hours every day reading newspapers or web sites (depending on which part of his career) and making sure he knew the news of the day, so he could yap about it.
People can run on and on about a subject and put together whole sentences and even use big words on topics that they simply do not understand at all. People can make firm, solemn declarations on science, economics, or sports almost as if they had a clue about those subjects. In the last 12 months we have been exposed to length discussions of virology and of constitutional law by people who clearly had absolutely no knowledge of virology or constitutional law. They just repeat something they've heard with no real thought. It supports what I want to believe, so I can say it and make it sound real.
Rush was like that, in my opinion. He didn't have a clue what he was talking about. He could repeat the phrases, but there was no comprehension. I have barely heard his show in the last year, since I stopped working at the office, but on one of the last shows I listened to, he explained that the coronavirus was just the common cold. He didn't mean it was no worse than the common cold. he said it was the common cold. And he said it like he meant it, and he repeated some words he had heard related to the word "coronavirus", and it made him sound quite intelligent, if you were no more intelligent than he was.
I just don't think he was very smart.