I specified redacting the details, i.e. the irc nickname.

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.