You're kind of correct on both guesses. You can get that change by changing the viscosity OR the airspeed. He elaborates later on, but you're changing the Reyn

You're kind of correct on both guesses. You can get that change by changing the viscosity OR the airspeed. He elaborates later on, but you're changing the Reynolds Number - a calculated value from the velocity, fluid density, viscosity and length. The cool thing about a Reynolds Number is that you get identical (in theory) airflow characteristics for two setups with the same Reynold's Number, even if e.g. the airspeed is different.