It's an older version of a replaceable event. For some reason i still see it. Replaceable events have always been a bit weird. I wonder if we should have never done them and stuck to plain old event sourcing.
Discussion
I think damus can be smarter and use the latest version of the same replaceable event like relays do it, or at least cache them and show an edit history, so you can see what version a user was replying to.