I'd put money on the Nano being 1/2 the SIZE and not power and she miss spoke, it happens on stage. Nvidia guys miss speak on stage also. What was I watching earlier, can't remember, some Swedish guy talking about the Unravel game(forget which conference it was, EA?) and he was literally trembling with nervous energy.
I'd bet on Nano being ultra binned but downclocked, down volted version of the Fury X. It's got a proper fan on it and due to the lay out of HBM pcb's you can get a lot more usable cooler surface area out of any pcb/slot size combination. I'd guess it will be in the 200-225W range and only 15% slower than a Fury X but would maybe run quite hot.
The non Nano will likely have the same pcb and design but the cooler will extend beyond the length of the pcb with a backplate/support bracket that extend the length of the card. It will run normal clocks, higher voltage and be higher tdp.
POwer/voltage/clock speeds aren't a linear relationship. You can quite easily drop 15% performance but significantly more than 15% of the power as a result.