True enough that today's electricity isn't all that green... but come on... where do you think hydrogen comes from? Fossil fuel to wheels, which is what all of them are (discounting nuclear and renewable in the electric mix), battery electrics are least pollution/CO2 of the three options.
If he means battery powered, we need to remember that the electricity to charge then battery comes mainly from fossil fuels. So in the long run it doesn't make a greener car - where does the battery go when it wears out? If he is thinkiing a new technology like hydrogen then maybe it could happen if there is a breakthrough in the next couple of years.
Tesla's prediction looks something out of reach today. But the technology sometimes moves at some unpredictable pace once it is out of its incubation period. The main hurdle in bringing Tesla's prediction to reality is the Battery -cost, range per charge and weight.
With some breakthroughs already in sight in this area , Tesla's prediction looks to be promsing enough to put one's bet on.
I think the term "fully electric" is the key here.
Cars like the Volt come close, but are actually hybrids. However, all it takes is a design like the Volt, however with a totally electric drive train (no weaseling about a mechanical link between engine and drivetrain in highway driving), and you have a "fully electric" car.
Alternatively, replace the ICE with a fuel cell, and generate H2 on board with a H2 separator, and that's also "fully electric."
What I do not see in the tea leaves is that battery technology is going to cut it, in 12 to 15 years, not as the primary energy storage device anyway. Battery electrics may become a little more prevalent, but their range limitations and "refueling" times are just too severe liabilities for general purpose cars.