It's probably simpler than this - advertiser just runs a campaign with some broad criteria (like income estimate based on IP-geolocated ZIP code) that both peop

It's probably simpler than this - advertiser just runs a campaign with some broad criteria (like income estimate based on IP-geolocated ZIP code) that both people in the same household fit. No surprise the same ad that one person had seen (and remembered) will be eventually shown to the other.