In a more general sense though not directly addressing the prof's argument. One insidious compounding of this, is with the "sunk cost fallacy".
https://www.behavioraleconomics.com/resources/mini-encyclopedia-of-be/sunk-cost-fallacy/
Thinking about this more, I suspect this econ prof's argument is on the mark in the case where one is devoting one's full attention to watching a show/movie.
I'm not entirely sure if this assertion is still true for the case where I am doing two or more things at the same time, where the tv is...