The article actually is forward looking and is making the point that oil demand is still growing and not yet falling. They cite and prominently feature this bit from the report the article is about:
"Oil use for cars peaks in the mid-2020s, but petrochemicals, trucks, planes and ships still keep overall oil demand on a rising trend. Improvements in fuel efficiency in the conventional car fleet avoid three-times more in potential demand than the 3 million barrels per day (mb/d) displaced by 300 million electric cars on the road in 2040. "
So yes, you are right fuel efficiency is a big factor; that's in fact exactly what the report says.
However, the article then goes on to claim that the report's prediction of electric car growth is actually off and that the impact will be much larger and much sooner than the report predicts. They also call out the notion that electric buses are currently already having a bigger effect than electric cars. I think they are right and that there are more currently oil intensive sectors where electrification is going to have an impact in the near future.
They then they get a bit hand wavy citing diesel demand declines in Germany that probably have much more to do with Diesel-gate and the sharp drop in demand in Italy, which in all likelihood has everything to do with the bad economy there and nothing whatsoever with electric cars. Also Germany is actually way behind in deploying electrical vehicles compared to e.g. the US, Scandinavia or the Netherlands.
In my view the real drivers here are going to be economical and not environmental. E.g. buses burn a lot of diesel. Diesel is expensive. Electricity is not. Therefore any reasonably priced electric bus is going to be saving cost. Which is why that is already having an impact.
The same is about to happen to most commercial operations involving cars. There are already police forces driving Teslas, which aside from being cool and good PR is also saving them a good bit on fuel. My bet is the taxi sector will start transitioning to being mostly electric in the next few years already. Fuel expenses are an enormous chunk of their margins. Same for local deliveries in cities. As long haul trucks become electric and self driving, that will also have a cost impact (eliminating the two single most cost factors of people and fuel). Aviation and shipping are next. That's starting to happen but will probably accelerate towards the end of next decade as technology matures. Also the economic life of such vehicles is much longer so this will happen slowly. But it's the same principle: fuel is by far the biggest cost factor and eliminating that changes the game.
Right now going electric doesn't quite make sense everywhere yet but that abruptly changes as volumes go up, prices go down, electricity becomes cheaper, and infrastructure gets deployed. By 2040 it is not even going to be close in terms of cost advantage. I'd actually say that by 2025 it is going to be very uneconomical to be burning fuel in cars (it arguably already is today); downright silly by 2030, and completely bat-shit insane by 2040. Somewhere in that time line any manufacturers still depending on internal combustion engines will be wiped out by a near complete collapse of demand and their profit margins. That's why essentially all of them are simultaneously investing heavily to make that happen while downplaying how fast it is happening so they can buy some more time to make it happen. They are all scared shit-less this will happen before they are ready to deal with it.
All this will also have an effect on oil production and related investments. In short, oil investors are already divesting. That cat is already out of the bag. Two things seem certain, decreasing demand and increased uncertainty over reliable supply and the resulting price volatility are going to be major concerns for anyone having oil as a dependency. It's not that there's not enough oil, it's more a matter of having an economic way of actually getting it to where it is needed at a predictable price.