Thanks. Yes, this is just how Mastodon renders content from Lemmy and Piefed at the moment.
Mastodon sees something that is not a Note, and says "I will treat it using a fallback mechanism. If it has a title, it is added to the top, I will add the URL back to the site at the bottom. If it has a summary, I will use that as the content"
Note that it does not use content, that's why there's no actual content. This is why the link preview also links back to Lemmy, not to the article itself.
nutomic@lemmy.ml and rimu@piefed.social can add this to their software, respectively, by populating summary. It can just be a copy of content, or it can be a summarization... or it could be the link to the article... anything goes really.