[euyyn]

> every link they every clicked on, on every web site. [...] No content from google was transmitted back to Bing. Just the next site the users went to.

Your theory cannot explain how Bing associated that "next site" with the specific search term the user had entered in Google.

If you had clicked a link on HackerNews, it wouldn't have shown up in Bing under some random search phrase. It's obvious that Microsoft parsed the search query out of the google.com URL, and the only reason why you'd do that is to mine what results were being presented for each search query.