Had you bothered to read the article you would have read in the first few sentences the following line:
"The survey comes after it emerged that two pilots on an Airbus passenger plane were asleep at the same time, with the aircraft being flown on autopilot."
I did read the article and saw that fact. Exceptions (both pilots fall asleep) are expected unless one takes better precautions around pilot exhaustion. Two pilots give one degrees of freedom tha a single pilot wouldn’t and it would likely be unpractical to have three pilots on long flights.
So we have the building blocks (two pilots) in place.