In defense of the coffin, I'd say this is not so much about a bug, but about reverse engineering real world effects of undefined behavior (as caused by a bug in software).
That is not the goal of mGBA (or any GBA emulator for that matter), btw. If you wanted to reproduce it faithfully, the emulator would be unusably slow.
You are trying to argue about the meaning of the words being used. This is not productive, as what matters is what the author of the argument meant when they used that word.
To be honest, I think it's about crossing the lines of emulation and simulation. In emulation, we mostly consider instruction level behavior as good enough, but here, we'll have to venture below cycle level and integrated hardware effects to copy the behavior.
