True, the sensors also have external pull ups. However, the sensor has a regulator to go from 5 to 3.3V. So, the sensor can be powered by 5 volts or 3.3 volts. It has pull-ups on both voltages. According to their description, the I2C SCL/SDA pins are level-shifted allowing for 3-5 volt logic. I think this level shifting is done with the BSS138 MOSFETs. With this, it should be fine to use 5-volt logic or 3.3-volt logic, but it didn't take into account my added on pull-ups. That's what concerns me.