[aslewofmice]

Judging by the pixels on their site, they likely used Google AdWords remarketing: http://www.google.com/analytics/features/remarketing.html

If you used the same computer from work that you used at home, you were cookied from work when you initially visited the site. Then when you were browsing the internet at home, the ad that was served recognized your cookie ID as the same visitor who visited the site and they can purchase that impression and serve their ad.