I don't know about that kid's theory, but the doppler shift can be HEARD.
If a train is coming at you blowing it's horn, the sound will be at a high pitch, but when the train passes you and then is moving away the sound will be at a lower pitch.
Whole galaxies are moving away from us, there maybe single stars whizzing around us, but all the galaxies (with all the stars) are moving always at ever increasing velocity.
MY PROFESSOR WAS EXPLAINING THE DOPPLER SHIFT WHICH MAKES STARS MOVING TOWARDS THE EARTH APPEAR MORE WHITE AND THOSE MOVING AWAY APPEAR MORE RED; A STUDENT RAISED THEIR HAND AND SAID YOU CAN ALSO SEE THAT ON THE HIGHWAY