After a brief research I found a few interesting facts.
Firstly: This HDR+ feature Google are applying in their recent phones is like an inferior version of certain aspects of the Nokia's PureView technology, reintroduced by another name years later (just like what Samsung did recently with their Always-On display, an inferior version of the Nokia's Glance screen). I am having every single aspect of the HDR+ (including the touch-focus and one-finger-zoom) on my Nokia Lumia from 2014 - two years and a half old. The only thing that the Lumia phones lack here is the laser autofocus which only advantage is faster autofocus in low/no light.
Secondly: DxO have never tested and reviewed any Nokia/Microsoft Lumia model since 2013 - the time of Nokia Lumia 1020 and 1520 (the latter having been tested in category "camera" and not "mobile" and - indeed - scored poorly).
Thirdly: DxO have also never tested and reviewed a single Huawei model. Ever. An underdog brand, indeed, but highly praised for their cameras and interestingly innovative technology, including a secondary black-and-white camera which takes the best black-and-white shots as well as helping for the low/no light shots with impressive results.
Conclusion: I have no idea what criteria DxO's tests and reviews are based on (I never saw a single night or pitch black shot in their tests and comparisons, nor did I a panorama or zoom-in shot). I also have no idea what criteria their choice of camera to test is based on, but the above mentioned facts - as other facts, mentioned by other people in the comments (like the flash and texture comparison between Pixel, Lumia 1020, and Nokia 808 and the respective scores, as well as the Pixel's test before its release, so that Google can include the results in their advertisement) are pretty odd and disturbing and I, personally, cannot count on any objectivity by DxO.
Never trust anything mainstream.