Well, that's not, what i meant. Please read my edit in post #14, i explained it in more detail. In short: your son forgot to log out of a google service on your laptop.
Please don't get me wrong, i'm no fan of google. I just don't think it's ok, from a thing that only happened once and only happened to you to come to that conclusion without making any further test. You can do the following 2 tests (with different search-terms of course): 1. if you still have all your cookies, use another IP address ( for example by VPN) and try the same. If it still happens, it has nothing to do with IP, it's cookie based 2. use a browser with absolutely no cookies and try the same (now with the same IP like your son again). If it still happens, you seem to be right. And also the question to all others: can anyone reproduce the behaviour described in the first post?