The Facebook app tracks location and other peoples' locations, and makes assumptions based on people being at the same place at the same time. If Facebook (or w

The Facebook app tracks location and other peoples' locations, and makes assumptions based on people being at the same place at the same time. If Facebook (or whoever) knows that several other people are all interested in new houses, and all those people + your girlfriend go to the same place(s), Facebook decides that your girlfriend might have the same interest as all those other people.