If the admin that received the email did not know how the domain was setup that is not google's fault. If they were paying for gsuite they could have and should have changed the default domain on the account. If they were using the grandfathered free version of gsuite they can't change it but they use the old domain for all logins so it should have rung a bell.
The only surprise to me is that the data doesn't go into a recoverable place for a short time instead of just wiping it.