Whether something is cheaper depends on market prices, in some places electricity is cheap enough to heat with.
Heating with fuel by burning is also efficient. Converting gasoline into kinetic energy via a combustion, on the other hand, has a loss of over 60%, whereas an electric motor may have less than 10%.
Still, what would happen if (as they article predicts) the oil prices tanked as a result of lack of demand? Driving with gasoline would be cheaper, making combustion engines attractive yet again. At the same time, wouldn’t the increasing demand in electricity caused by electric cars raise electricity prices? Absent of government intervention, the market will find a balance of both technologies.