I agree. So Google knows my phone connects to a certain IP address thru Wifi, and can link this data to other devices on the same. The problem is it does not know that my device may belong to the same IP address due to portability, unless it is looking for number of connections and such.
It would be interesting experiment to see if I asked a friend or family member to do several searches on a home device. I take my device and connect to their network and see if I get ads for mine or their searches