Should I be upset, or is his explanation correct? I was looking at the history on our family laptop...?

[YFCSOnline.com]

Visiting certain sites may contain ads that do popups. When this is done a cookie or temporary file is planted on the history of the computer. I wouldn't worry too much. You could visit some sort of clean christian sites sometimes and an ad will bring up really horrible images or bad things that you wouldn't expect. He may have visited Facebook, Twitter or Myspace. Doesn't really mean he has an account on their but sometimes if you look things up on forums their could be links to them or even Videos for them. I know some how to videos will do this sometimes.