It's a joke - the real world is generally continuous at the scales of our perceptions, but our perceptions can make errors like not seeing a car off to the side then suddenly becoming aware of it and swerving or screeching to a halt. I think it comes under the rubric of "if you took calculus and then pay attention to your own life."
It's actually real. IIRC, our eyes and focus move not smoothly, but in discreet jumps. Objects can be overlooked. I think I read that they train professional 'drivers' like pilots how to compensate.
