One, maybe you actually tapped on something that was related or even searched for that product online on a website, maybe before you had that conversation. We actually do work with advertisers who share information with us about who is on their website to try to target those people with ads. So if you were looking at a product on a website, then that advertiser might have paid us to reach you with an ad.
Two, we show people ads that we think that they’re interested in, or products we think they’re interested in, in part based on what their friends are interested in and what similar people with similar interests are interested in. So it could be that you were talking to someone about a product, and they, before, had to actually looked for or searched for that product, or that, in general, people with similar interests were doing the exact same thing.
Three, you might have actually seen that ad before you had a conversation and not realized it. We scroll quickly, we scroll by ads quickly, and sometimes you internalize some of that, and that actually affects what you talk about later.
Four, random chance, coincidence, it happens.