I wonder if it is also possible they associate you with searches your friends have done after being in the same location? So if you chat about going to Bali with your friends or co-workers, and one of them searches for Bali flights, they then display Bali ads to the entire group.
This is true, they are known to monitor location all the time and display ads like this. They will also suggest people to be friends if they find you guys hang out in person a lot.
