Well yeah, that's exactly what it is: A very short Fury X with lower clock speed and therefore lower power consumption for the same price. As you say, there's literally no reason to go for the Nano unless you need a short card, and that's exactly the market its placed in.
Now that I think about it, it may actually be pretty smart of AMD to use the regular Fiji chip instead of having a different one just for the Nano, because it lets them adapt the supply of Nanos and Fury X cards to the demand. If it turns out that the Nano is more commonly used in a few years, they don't have to change anything about the chip manufacturing volumes, they just have to put the chips on different PCBs.
Now that I think about it, it may actually be pretty smart of AMD to use the regular Fiji chip instead of having a different one just for the Nano, because it lets them adapt the supply of Nanos and Fury X cards to the demand. If it turns out that the Nano is more commonly used in a few years, they don't have to change anything about the chip manufacturing volumes, they just have to put the chips on different PCBs.