This is normal. You're just misunderstanding what a user and group is. That's all.
In Windows, you have users that are members of groups. For example, your administrator account is a "user" that is a member of the "administrators" and "users" groups. A standard user account would be a "user" that is a member of only the "users" group instead.
If you like, the tutorial below can help show you the differences and give more details on users and groups. User Accounts - Add or Remove from Groups