Its less an emulator, and more a translation layer.

Emulation is when you essentially construct a virtual representation of the target hardware, and map the virtual hardware to real hardware, and then you can run code made for the emulated, target hardware, on the real hardware.

A translation layer does not involve emulating a specific target hardware configuration.

WINE -> Wine Is Not (an) Emulator

Proton is basically... a massive expansion pack, for WINE.

Proton translates Windows x86-64 calls into Linux x86-64 calls.

FEX translates Linux x86-64 calls into Linux ARM calls.

The point is actually to be able to run Linux x86-64 on ARM, not the other way around.

But, as a consequence of developing a comprehensive ARM <-> x86-64 translation layer, that does mean that it will be easier to port APKs, Android libraries, or in some instances just run APKs, on x86-64.

EDIT: Fucking derp.

FEX is an emulator, because it is mapping to another hardware architecture.

https://github.com/FEX-Emu/FEX