I dont know if there is a username involved, but there is a wallet naming and a password to encrypt the wallet. These are only required to access the wallet on the device where it already loaded up. You will not need them on a new device where you want to load up your wallet again. There you will need the seed phrase once again and after that you can encrypt that wallet with a different password.
The user perhaps implied about the name of his wallet file.
I did not see people mention about another backup method, the wallet file.
Ideally, the wallet seed phrase must be backed up first because with it, a wallet owner can recover the wallet anytime, on any new device.
Secondly, he can use the wallet file as a backup but it is a digital file and will need a password to access the file and private keys in that wallet. So if he has a wallet file backup, he will need a wallet password.
With a wallet seed phrase, when recover the wallet, he can set up a new wallet file name and a new wallet file password. Wallet seed phrase is most important for backkup.