Knowing there will be a peak is different from having the ability to always have low carbon power to put in the grid at the peak.
Back in the day. we didn't worry about bringing another coal fired power station online for the ad breaks in "The Price is Right", but nowadays, we'd rather not do that, especially for a short period (I do recognise that it's more likely gas nowadays for transient peaks).
The paper is observing that if the peak was lower, by having a little more randomness in the demand, there would be fewer problems supplying the overall demand as it would be spread over a greater period of time.
Biting the hand that feeds IT
