My assumption (I no longer work at Google, and I didn't have anything to do with this part of the infra) is that Google uses IP addresses for ad targeting (and

My assumption (I no longer work at Google, and I didn't have anything to do with this part of the infra) is that Google uses IP addresses for ad targeting (and other targeting). In fact I think they announced this recently, but I believe they were doing it before. It is also possible it was coincidence in your case, but I doubt it.