The batteries are charged by plugging the car in to the mains.
Any miles travelled on this energy surely can't be counted as MPG as the energy is gleaned from elsewhere.
I could carry a can of petrol on a pushbike and claim infinite MPG as none would be used.
My thoughts are that it is in line with the other claims made by "green" energy vehicles. Any electric/hybrid which claims zero or low emmisions doesn't take into account the coal or other fossil fuel burning power station that provided the power with which it charged its batteries.
For example, I could have bought a Nissan Leaf for €22k, but instead bought a Hyundai i10 2009 for €7k which gives me €15k to fill the tank.