Hmm... I wonder if that was written before it started federating?
Maybe the Write Freely website has something about it? (https://writefreely.org)
By the way, someone in the thread I linked to said that on their fork of Mastodon, the entire Write Freely article is visible instead of just the link.
So maybe it's down to the platform you're on to decide whether it just shows the article link or the entire article?