That is not pentile, which has to do with the pixel layout and not what you're seeing. What you're seeing is the digitizer grid under the display. I don't know the technical specifics, but I think it has to do with how close the digitizer is to the screen and inherent with LCD displays like the one on this phone. The Nexus 4 had the same thing, as has other phones with LCD displays like some from HTC. I remember my old HTC View having the same effect under the screen.