Those posts are many years old. Some time back the state of California made it illegal to ship with default name/pass. Since then Jetsons don’t have defaults, but upon first boot you can set up your account name/pass.
Old boot flow was flash, and it then reboots and optional software was added over
ssh to via the default logins. The new flow is flash, reboot to complete the name/pass, and then JetPack/SDKM uses that name/pass which you just created to install optional software via
ssh. FYI, there is no reason you couldn’t make your initial account setup the same name as the default one, although you wouldn’t want to use the default pass.