So Polaris 12 IS a thing as AMD's Alex Deucher added support for it in their open source code repository. Apparently nothing fancy was added. Mean while nothing on Vega which should be launching soon...
So on the Linux side of things, there's no significant difference in software support between Pascal and Maxwell. It's looking like Vega will be the same way. And a 64 CU Polaris chip would benchmark about the same as that Vega demo.
Edit; another theory is that it is an OEM specific card based on Polaris 10/11.
Edit #2; it just occurred to me that this is probably a fully unlocked Polaris 11 and RX 465. RX 460s are 10% locked IIRC.