The article describes how he created a layout based on optimizing 'rolls', which is (I think) the same as piano runs as you describe: striking keys in sequentia

The article describes how he created a layout based on optimizing 'rolls', which is (I think) the same as piano runs as you describe: striking keys in sequential order across the hand. So for example 'the', 'you', 'in', and 'as' are all struck with adjacent fingers, just as you would play a piano or (as he describes) drum your fingers on a table. He very much considers this important factor as the critical component of the layout he describes.