It's worth reading the details set out in the article.
Selectively quoting, and adding approximate MPGimp figures in red:
Converted to standard fuel consumption figures using the lifetime average kWh per kilometre, the BMW i3 came in as the most efficient, recording a fuel consumption rate of 4.392 litres/100km (64mpg) – about the same fuel efficiency as a diesel BMW 3 series.
The Tesla models, while scoring higher than the BMW i3 (between 5.011 to 6.014 L/100km (56 - 47mpg) for the Model S and 5.689 to 6.957 L/100km (50 - 41mpg) for the Model X) came significantly under similarly sized vehicles in their range (for example, a diesel Holden Commodore does 5.7 litres/100km (50mpg) while a VW Touareg diesel SUV does 7.2 litres/100km (39mpg)).
Selective comparisons if ever there was one, Holdens being known for their complete disregard of fuel efficiency. Instead for the larger vehicles:
Mercedes-Benz A Class A200CDI 4.0l/100km
Peugeot 5008 GT 4.8l/100km
Audi Q5 40 TDI quattro 5.3l/100km
And smaller vehicles comparable to an i3:
Peugeot 308 GT 4.0l/100km
Audi A3 Sportback 1.6 TDI 4.1l/100km
Picking selectively for efficiency makes the picture entirely different. Noting that they still ignore the emissions restrictions on the cars, and claims the opposite:
But is it green? It’s better than putting diesel in a car, says Edwards, because the constant running rate of the gennie uses the fuel more efficiently than idling and accelerating in a car.
So it uses more fuel in an engine with looser environmental restrictions, and is somehow "greener". No, no it isn't.