No, its just an utterly over engined car - 4 liter superharged with an auto box.
Design from the 90's actually :-)
And built for luxury, not fuel consumption.
Typical figures suggest that a small equivalent 100bhp 5 door town car - something like a Fiesta..is replicable with about 50Kwh for 200 miles range.
At 50mph average, an average drain of 12.5kw. About 16.7bhp.
If one thinks it might do 6 times that power to do 120mph continuously, then its got 20 minutes 'in the tank' - or about 67 miles 'in the tank' One third of the fuel consumption. I think that is probably about right.
I think that is very reasonable. Anyone who has actually really stirred a car around knows that at the best, you can use full power about 70% of the time, the rest is braking for the next corner..unless you have a car geared to achieve max power at max speed and hit the autobahn..
One of the major reasons that diesels are so mpg efficient is that they are most efficient at low throttle settings...petrol tends to be far less so.