Ahhh that was a thing because there were way more drives (Episode edited backgrounds were still allowed to be publicly distributed) and people would just download backgrounds and not know who made what or who to credit for what. So they would just put it permanently on their Instagram highlight.
But this is only a “rule” for some background creators now. I don’t think everyone has this. It’s better to just credit in the story so people can actually see the background/overlay.