New top story on Hacker News: Ask HN: I bought Voltaren at the chemist, now Google shows me ads for it. Why?

Ask HN: I bought Voltaren at the chemist, now Google shows me ads for it. Why?
20 by wideareanetwork | 19 comments on Hacker News.
How does google know I bought Voltaren? Is my bank purchase history shared with google somehow? I guess it could just be coincidence?