I find it slightly amusing that they do not need to register a domain name for that one.
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Because the BRs say that the subject Common Name, if present (which it usually will be for really crappy software that still doesn't implement standards from _last god-damn century_) must be chosen from the list of SANs, these certificates will have an IP address as their CN, plus an ipAddress SAN.
Here is an example, which my records say had an IP address as its only name, but at time of writing crt.sh is timing out for me so forgive me if this some completely unrelated cert and I've pasted the wrong one: