What is that meaning of "This Sensor uses 5v as a working Voltage only"?
Typically, an IC's input and output logic is tied to the IC's power. A 5V IC will typically have GPIO that are 0 to 0.2 * VCC for logic Low, and 0.6~0.7 * VCC to VCC + 0.3V for logic High. This can vary, but its a good rule of thumb.

Sometimes you will see a 3.3V IC module have it's own regulator, and it expects 5V, to the module, but it will either expect 3.3V logic, or need/provide a logic-level translator.

The Module you ask about is the second type. It has it's own 3.3V regulator. It also provides logic level translation, using a pair of mosfets on the i2c lines, allowing you to connect a 5V i2c signal to it's 3.3V i2c signal.