Do you have location tracking turned on? I feel like a few times when people looked into this, it came down to the Taxi app having location sharing on (so the app can show you fairs, of course) and that the fact that you wrote something about needing a taxi is irrelevant because the app knows you are someplace where you might need a taxi.
And maybe someone nearby you who also had the same Taxi app had just booked a trip. They can correlate your location and people around you.