Not that 50% of all web content is AI generated.
On the contrary. It explicitly states that it is.
To quote - "It found that most of the internet is translated, as 57.1 percent of the sentences in the corpus were multi-way parallel in at least three languages. "
So in other words, that majority of web content is AI translations of other content. As its often poorly translated, or entirely mistranslated, it qualifies as "AI-generated garbage" - hence the headline.
Someone should invent a search engine that allows for curated sources. For most things, I'd love to search among the top few thousand sites, and exclude everything else.