Doesn't explain why efnet themselves are not at fault for failing to redact the details if they are so concerned. What if the attacker was Hetzner staff?
When contacting ISPs some people attach contact information so that the ISP can request more information, maybe even make a call to verify identity and discuss the matter to help resolve it.
This doesn't mean that the information is intended for the abuser himself. I'd expect the ISP to send anonymized information/questions to the owner of said service, and not just forward "everything" (especially without discussion with the reporting party).
Reporting DDoS and abusers risks putting a huge target on yourself, your company, your servers, etc.
That is what the issue is about.
If the information within the headers is that sensitive, the headers should probably not be forwarded from efnet to hetzner. At its most basic their servers are attacking efnets and so should be considered hostile.
By all means pass on contact information to resolve amicably - but don't leave sensitive information.
There's no reason to pass on irc nicks or sensitive email addresses - what use are they to hetzner? I have the same expectation of efnet as you have for the ISP.
If the issue is that efnet is being identified as the reporter to the rogue attacker, then that is not what is stated in the efnet admin's text.
You seem to misunderstand the situation.