So he didn't register the name-servers as such, just the domains that point to them.
Slightly strange though, it's unusual for a name-server record to be on the root of a domain, normally you'd have an A record, such as ns1.domain.tld pointing to each name-server, but in this case the .io namespace was including domain.tld as a DNS server. Seems a waste of a domain.
The other ones, on the nic.io domain are more conventionally set up.
Biting the hand that feeds IT
