indyank - 3:12 am on Nov 15, 2012 (gmt 0)

And is there a way Google could tell that most of your traffic is coming from them?

Their products like Google Analytics, Google Adsense and Ad planner, Goggle Trends etc. can easily determine your whole traffic. In addition, they can use third party (supposed to be third party sites for the general public) data like those from ISPs, toolbars and other external sources.