and yes, the ‘Play on Awake’ box is not checked.
EDIT:: if you’re having this problem, just keep watching the video to the end 
private void OnCollisionEnter2D(Collision2D collision)
{
GetComponent().Play();
{
Do you have an audio source on the paddle by any chance? because it will trigger a sound.
in unity, select the ball and look in the inspector at the audio source. There might be a box which says “Play on awake”. If this is checked, uncheck it.