That title is clickbait.
From the article:
In 2020, the Computers in Human Behavior study provided additional insights into the tactics employed by corporate trolls on Reddit. The study focused on the top 100 subreddits, analyzing the content posted within these influential communities.
The results were alarming, with 15% of the top 100 subreddits found to have content that was likely posted by bots or corporate trolls, specifically aimed at promoting certain companies or organizations.
That's 15% of the top 100 subreddits contained some content that was likely posted by bots or corporate trolls.