As far as I can see, Google provided a search-result, which eventually (after Google's batted it around internally a few times) turns into an HTTP request to the CBS website, which resulted in password-free access to a public document.
So that will show up in the CBS webserver's access log; that's how they got the IP address. Nothing to do with Google.
Getting from the IP address to the person is messier; websearches, requests to ISPs, and presumably searches of activist databases the cops no doubt maintain might all have played a part.
My guess is the cops knew there was no case against him, because they tried the URL, and saw that there was no password challenge; but charged him anyway, because he was an activist, and they wanted to intimidate him.
> Hutchinson said his identification by Leathermarket and subsequent arrest raised questions in his mind, saying police confirmed to him that the company had handed over an access log containing IP addresses:
Edit: Whoops, all of my assumptions were wrong!