Why is the fuel efficiency of the Audi A2 compared to other cars in its class?

I've heard that the Audi A2 has great fuel efficiency, but why is this the case? What makes it stand out from other cars in its class in terms of fuel efficiency?

The Audi A2's exceptional fuel efficiency is a result of its lightweight aluminum construction, aerodynamic design, and efficient engine technology. Together, these features allow the car to achieve higher fuel efficiency compared to other cars in its class.