There's hundreds of gameboy emulators available on Github they've been trained on. It's quite literally the simplest piece of emulation you could do. The fact that they couldn't do it before is an indictment of how shit they were, but a gameboy emulator should be a weekend project for anyone even ever so slightly qualified. Your benchmark was awful to begin with.

Is such an emulator not part of their training data sets?

As coding agents get "good enough" the next differentiator will be which one can complete a task in fewer tokens.