YouTube user Tim Rutledge is much like any other hardware consumer, except in that he probably actually read the manual for his washing machine. Turns out, pressing the right combination of buttons on this specific model activates a command to play the American, New Zealand and Australian National Anthems.
According to commenters this particular one is a Fisher and Paykel washing machine. As you may have guessed Fisher and Paykel is New Zealand based brand. Looks like this is what appliance engineers do when they get bored.