Neither you or your parent is incorrect; this behavior is variable. I setup 8 new win10 boxes last week, 2 of them (HP, the others were Dell) required pulling a lan cable to get to the local account setup. I didn't have time to check details to see what was different (I'm not really IT, but small company/many hats) but the local account option didn't appear until the internet was disconnected.
Windows 10 Pro, I've installed it about 40 times or more. Domain Join is the option to create a local account. It works, I do it every install, while connected to network.