The calculation they have used is based on where the glass meets the bezel and not the active pixels of the LCD. From the active pixels to the edge it's roughly 2mm. Deducting that it's about 86.5%.
But I'm like most people, who cares. Just look at Marques, he's like a little kid with his first BMX.
But do we know if the 91% ratio came from reality or the render though?