I don't see mis-fueling as the root cause of this incident. That's not going deep enough.
I see the physical possibility to mis-fuel as the root cause -it is physically possible to put the wrong fuel in an aircraft.
The only measures preventing misfueling are administrative; that is, training of pilots and refuelers and marking of aircraft, pumps, tankers, etc, to attempt to ensure that the correct fuel comes out of the correctly marked pump or tanker and goes into the correctly marked aircraft filler.
In the hierarchy of hazard controls, administrative controls, which rely upon humans not to make mistakes, are a poor substitute for engineering controls which make it physically impossible to make the mistake in question.
Think about it: cars the world over which run on unleaded petrol (gasoline) have
special smaller filler necks and a physical flap in the filler - and that's just to prevent even small amounts of leaded fuel contaminating the tank and poisoning the oxygen sensor and the exhaust catalyst.
This is standardised across hundreds of millions of cars, in a world where
leaded petrol was eliminated by 2011. If the car industry can achieve this, why can't aviation come up with an engineering control preventing mis-fueling?
Now one response would be to point out that petrol cars, which cannot tolerate lead, but can tolerate misfueling with diesel fuel without damage, have the limiting filler, while diesel cars, which are readily damaged by fueling with petrol, and are probably more likely to be misfueled by drivers familiar with petrol cars, are not protected. This is correct, and is a consequence of the need to retain backward compatibility with existing vehicles and bowsers, as well as high volume diesel pumps.
But for aircraft, this is potentially a matter of life and death. The numbers of fillers and bowsers is far smaller, and the ratio of the cost of the fillers to the value of the aircraft is probably lower. Aircraft are regularly subject to regulatory requirements to make modifications as design issues come to light.
Would it really be that difficult to develop special shaped bowser nozzles and filler orifices to physically prevent misfuelling?
As a side note, about 20 years ago, I helped a friend fit a small turbo diesel motor to a Suzuki Sierra "jeep" style 4wd, previously fitted with a (leaded) petrol motor. He often got comments from service station operators.
On one occasion he arrived at a remote roadhouse (Australia), stopped, looked around for the diesel bowsers, finally found them in the section with lots of room for road trains, and went and filled. When he went in to pay, the usual discussion about diesel into a Suzuki ensued, and the cashier commented "I was going to get on the PA and warn you that you were filling with diesel, but you looked very determined to use diesel..."