It actually shows half of the post followed by …, making you think that by clicking it you’ll see the rest. But then you get taken to the App Store to download Threads.

That explains it, I'm not in that ecosystem but suspected it was something similar.

Likewise, I wouldn't be shocked if I'm counted as an daily active Instagram user, despite not having an account or using it directly. The "shorts" are embedded in FB and occasionally interesting.

Feels a bit misleading by FB