Hmm - after reading through the review, I'm not sure how their scoring really works. Android phones have had superior daylight photos for a while now due to the MP race and similar sensors. iPhones have generally always been much more usable due to their excellent/fast auto-focus and being good in both day and low light. The Note 4 is one of the few phones I've found that can go toe to toe in all conditions, though auto-focus is still slower (one area the S6 looks much better in).
Reading through both reviews on that site, the Nexus 6 camera seems just like every other Android flagship from 2014 excluding the Note 4. Great in daylight, not great in low light, and relatively slow auto focus. The Nexus 6 scoring the same as the Z3 which has issues of its own in still photos also makes their scoring system odd.
Again, not disputing the Nexus 6 has a good camera, but their samples and commentary echo the subjective experience I've had - it's good, but not great all-around as low light makes up at least 1/3 of my use. I don't even mean to argue the merits of the camera, but putting too much stock on some end score by one site seems a bit like confirmation bias.
iPhone 6 Plus low light:
Nexus 6 low light: