But WINE isn't designed to be interoperable with Windows. I'm not even sure what that means. Outside of some special cases, it's not like you can get something

But WINE isn't designed to be interoperable with Windows. I'm not even sure what that means. Outside of some special cases, it's not like you can get something useful (or even functional) by arbitrarily mixing and matching Windows and WINE components. Instead, for the APIs it supports, WINE was designed to interoperate with Windows programs (binary and source) in same kind of way the Android Java environment interoperates with Java programs (again both binary and source) for the APIs it supports. There are some minor differences (e.g. WINE works with binary applications directly, Android requires that Java bytecode be compiled to Dex bytecode, etc.) but the overall structure is the same. Sure, Android only supports few Java APIs and WINE supports tons of Windows APIs, but that's the distinction fair use hangs on, how does any re-implementation of a proprietary API ever get off the ground (legally anyway)?