I probably was wrong and most probably the user visited the shopping place of the item, which probably would have a facebook javascript library.

But there are ways to get information of you browse history:

with a facebook like button (other facebook library, or google analytics), which it is in almost all websites, you have the previous web.

There were bugs before in browsers that exposed the previous history (sorry I cannot find the link)

You could have an extension in your browser that analyzes the whole history.

You can also get information by opening an iframe and accessing other site cookies.

Doing history sniffing (although unlikely)