It makes sense, as it identifies the specific (medium-hosted) blog as the source, rather than just the hosting platform.

I think this is a new feature (at least, I haven't noticed it before), and seems to apply to some other domains as well, such as twitter.com and github.com.

This is a fairly recent change on “platform” sites like Medium, Twitter, and GitHub. It’s quite nice for browsing the history, in my opinion. I like how HN keeps getting minor improvements like these without a big redesign.