after disc utility erase it askes for firmware password

Before I sold my MacBook Pro I went into Recovery Mode used Disc Utility and erased the internal SSD then downloaded Catalina and it installed it on the internal SSD. The buyer set up the computer as the new administrator. Then complained that my Photo’s were on the drive. Little did I know that Catalina changed things on the system drive by splitting into 2 with Mac HD and Mac Data HD and if you click on Mac HD and erase the drive you will leave your data on the computer. So after research I found that in order to erase everything you have to click on the Erase Volume Group. Thanks Apple. Now the buyer says when he starts the computer up a BIG LOCK appears and asks for a password and it won’t accept his System Password and he’s locked out. He thinks it’s asking for a Firmware Password which is very long. What’s Going on is The Question.