If you haven't set up an Address Book card for the email@hidden address yourself, Mail will glom on to some name for it on some piece of incoming mail. I expect it's deterministic but I don't know what the algorithm is.
I have an address book entry for the list, it doesn't have "XCode" in it, and I still saw that. According to Mail the raw source contains:
Date: Thu, 01 Feb 2007 09:08:09 -0800
From: Chris Espinosa <email@hidden>
Subject: [ADMIN] Monthly Reminder: How to Ask for Help on xcode-users
In-reply-to: <email@hidden>
Sender: xcode-users-bounces+larry=email@hidden
To: XCode Users <email@hidden>
Errors-to: xcode-users-bounces+larry=email@hidden
Message-id: <email@hidden">email@hidden>
Are you saying my copy of Mail is responsible for that "XCode?"