That's not quite a correct summary of their methodology.
They're indeed starting from that $100M/year, and scaling it up directly by revenue growth. But Google's revenue didn't grow by 47x in that time. So the number they end up attributing to Google News is $700M/year, which is still pretty ludicrous for a site with no ads nor other kind of monetization.
Where does the missing $4G come from? Well, they assume that Google Search does 6x the news traffic of Google News, and then apply that 6x factor to the fabricated $700M number too.
They're indeed starting from that $100M/year, and scaling it up directly by revenue growth. But Google's revenue didn't grow by 47x in that time. So the number they end up attributing to Google News is $700M/year, which is still pretty ludicrous for a site with no ads nor other kind of monetization.
Where does the missing $4G come from? Well, they assume that Google Search does 6x the news traffic of Google News, and then apply that 6x factor to the fabricated $700M number too.