Looking at the inode level doesn't really change things. The filesystem stores information about the file including the numeric group ID for it in an inode. But that still isn't linked to the user account in a "live" fashion. Once the file is created the information is set. You can change the default group for the owner, but the file (and the inode) still doesn't know about that. You need to use a command like chmod or chgrp to edit that information.

You could use switches on an ls command to get more information about this. Maybe making a test account, homedir, and some files then playing around with it would help make it more clear. For example, in solaris ls -n will print the numeric group and user IDs instead of the names of the group and user. Also -i will print the inode number as part of the long listing.

I'm not sure if that answers your question, but I think it should.