I get what you're saying -- that the link source indicator should point to the instance that hosts the group -- but it's a quirk of how federation works that the thread is actually on kbin.social. And, well, any other site that's following the thread.
Everything is actually local on the fediverse. It's just that not everything has to originate from the local website. Federation works via content mirroring, which is why the URL for any given Magazine you're viewing still starts with kbin.social. You're not viewing remote content, you're viewing local content that was imported from a remote source. And the link indicator is telling you where kbin has been told the content resides.
And that's on kbin.social.
I think maybe the link source indicator just shouldn't render if the thread doesn't have a link purposefully attached to it, and the Magazine name should show the full name@host indicator.