Well... just going off what we know now, I am sure that it'll be a great phone. First, the sensor is a slightly upgraded one that is in the 6X... (IMX377 vs IMX378). I am not sure what Sony did to tweak the sensor though, most likely something minor. The IMX377 was still the best performing raw sensor on the market.
So... the Pixel. Google and Qualcomm worked together to farm off the image processing to the ISP... So in terms of shutter speed, the Pixel can rip off an HDR+ photo in less time than the 6P could take a standard picture. That is the killer detail. HDR+ is a marvel in terms of processing. The HDR+ pics coming out of my 6P are better quality than what my wife's Note 7, her S7 and her G4 did. So... the Pixel took that picture quality, made it fast, and added in top shelf stabilization and improved processing due to the new ISP junk in the SoC.
No shock that it popped that high a score.