What? He asked Johnson sensible questions, and Johnson didn't have answers. This is the sort of thing that should happen at the big debates and usually doesn't. Often the candidates aren't challenged when they respond with no substance to policy questions. Johnson was pressed and he couldn't handle it.
He asked about taxation. Johnson told him what would likely happen if he were in office, what direction he would hope to sway the congress, and what would be a realistic scenario. But he didn't like that answer, so pushed further into the "If you were all powerful" scenario, which Johnson gave his honest opinion about taxes in general, namely wanting a federal consumption tax. Then the guy insulted him and continued to badger about abolishing taxes (he says it about 8 times.) Johnson responded with hostility. Hardly a surprise and I don't see how you can accuse him of not having substance when his first answer was very clear in what he would do if in power in regards to taxes.
As an aside, the interviewer is wrong about the consumption tax being panned by economists (although really, he avoids addressing it by just harping on abolition.) Greenspan suggested the same thing a decade ago.