I think you did a great job with the research here, so I commend you for taking the time to look up and cite sources.

The one catch is that "specific hardware" doesn't clearly indicate that he's referring to the "sensor", and I actually suspect the Google dev is referring to the low power coprocessor/sensor hub. In other words, the sensor can read whatever finger print or gesture, but the phone needs to be able to interpret that as a swipe.

We know that the SnapDragon 820/821s have an improved DSP with a new low power sensor island (see the second to last and last image on this). And so in the same way that the introduction of the first generation sensor hub allowed for things like Ambient Display and "Google Now" with the screen off (with minimal power consumption) that distinguished the Nexus 6 from the Nexus 5 even though from a hardware perspective, the motion and microphone sensors were all there, I suspect so goes the same with the new, next generation Sensor Hub in the Snapdragon 820/821.