The author is a career journalist/digital publisher with lots of professional contacts in the industry. He has spent lots of time investigating digital media business models and the financial health of digital media companies. His own company has transitioned from being mostly ad supported to being mostly directly reader supported in the past few years.
He is just making a blog observation, which can be best read in the context of the rest of his site/blog, which have been talking about similar issues for years. Much of his evidence is scattered through tiny posts, which blog readers are assumed to have been following. It’s not supposed to be a deep carefully cited research article.