I think people were entering the SMS short code the digits were sent from instead of the digits so they wanted to make it clearer that it was 6 digits they want you to look for.
When I get sent a verification code from myGov (via text message), the message contains the 6 digit code, AND a 6 digit phone number for the help desk. I have to stop and double check which is the code, because I have accidentally entered the phone number many times.