That message appears when you are trying to delete an account that still has domains connected to it. Remove the domains from the account vis the control panel before deleting the account.
They are the same thing. Either the domain is assigned to an account or it’s not assigned to an account. If it’s assigned to an account, it cannot be used on any other account, even if the account it’s currently on is suspended or deactivated.
This is why we show the warning screen when deactivating your account: if you want to use the domain on another account, you need to remove the domain from the account first.
It’s not. There are other reasons why your domain may redirect to suspendeddomain.org other than the account being suspended.
We have an article listing all possible reasons, and it has a section “You are moving the domain to another InfinityFree account”.