They listened to users searching anywhere in any search engine, and just storing the correlation (search term → clicked website). Google actually does the same

They listened to users searching anywhere in any search engine, and just storing the correlation (search term → clicked website). Google actually does the same, through their own analytics. It's just that so many more people visit Google than Bing or Yahoo that automatically 90% of the (search term → clicked website) mappings are recorded on google.com