You wont be getting 70 MPG, I can assure you that.
Google is grabbing official figures that Fiat have put out (and not necessarily for your specific model either). More often than not, these figures are obtained in ideal conditions which massively inflate the MPG numbers.
As far as the 70 MPG figure itself, that is also wrong. The 1.2 Fiat 500 official MPG figures range from 58-62 MPG . In the real world, you're going to average out at around 45 MPG. The only models that will get anything close to 70 MPG, which should come at no surprise, are the 1.3L diesels, which average out at about 60 MPG in the real world.