> the reason the riemann hypothesis is important is because it is the reimann hypothesis
I can see this being a joke. Entire subfields of mathematics have been built on the assumption that Riemann hypothesis is true. He probably assumed that everyone in the audience would know this, which is not unreasonable.
Try "Trolling Euclid" book by Tom Wright, to understand why the Riemann Hypothesis is considered by many mathematicians to be the most important unsolved problem in mathematics today.
I can see this being a joke. Entire subfields of mathematics have been built on the assumption that Riemann hypothesis is true. He probably assumed that everyone in the audience would know this, which is not unreasonable.