I've turned my personal website into a read-only relay (using khatru) that generates kind 30023 events for all the old blog posts I've written in the past upon demand. My domain had never hosted a relay. There was no hint of it anywhere. I didn't tell anyone about it.
And yet less than a day after putting it live some of the articles there were being propagated to other relays and some people were commenting on them. How do you explain this?