How do I2C modules select between more than 2 slave addresses?
I think that the sensor can differentiate between hard Vcc and ground, as opposed to SCL and SDA, which only have pullups to Vcc. During power up, the device can test A0 sending test data through SDL, then through SDA. If A0 is always zero no matter what the test data, it is connected to GND. If it is always one, it is connected to Vcc. If it follows the status of any of those outputs, the device can know what pin A0 is connected to (SDL or SCA).