I just crossposted something using Thunder and another user let me know that my crosspost did not show that the other post was the original.
See here: https://lemmy.ca/comment/11901004
Not sure how that can happen but seems like a bug in Thunder then?
That’s probably the main difference here.
The web UI does not show the age of the crossposts, so I guess the devs used the “let’s inject the source in the body of the crossposts” as a workaround for that