This is some guy's masters thesis. Sadly, guy may have spent more time on web design than analysis.
Nonetheless, there are a few interesting details.
Chatbots are bullshitters
Instead of “hallucinating”, AI systems can be better understood to be bullshitting – generating plausible-sounding text without regard for truth (Gorrieri, 2024; Hicks et al., 2024; Trevisan et al., 2024). In this sense, generating slop is also bullshitting: communicating something not for its informational value but for its effect (e.g., engagement on social media).
To heck with your em dash heuristic: negativity is a sign of humanity
The most noticeable difference occurs in the distribution of sentiment across slop and non-slop, as there are almost no slop news articles with negative sentiment.