Yes. If you visit someone's home and connect to their wifi, every app on your phone can record that you are there. They record the other people that are there

Yes. If you visit someone's home and connect to their wifi, every app on your phone can record that you are there. They record the other people that are there, too. If one of those people has been reading websites about topic X, the ad networks record a high interest in that topic. It makes sense to advertise X to the people close to that person.