Turns out Nintendo's emulator never emulated the SuperFX chip. The RA developer did some sleuthing and found out about it. Even Nintendo knew they couldn't run Star Fox on the VC, yet, hackers did. Sad
Whoever told you that's full bullshit. Bsnes and Snes9x play the game perfectly (Bsnes is the most accurate and Snes9x isn't terribly far behind). Zsnes can run it too, but it locks up a randomly due to buggy emulation and plus it's old as hell
Simple, it was being played on an outdated emulator, in this case something like Zsnes. The major problem is it was written in ASM (assembly) while using various emulation hacks to make it run as fast as possible on older hardware. As a result, many games ran improperly, froze, ran too fast, etc. In this case, Mario RPG used the SA-1 chip, but Zsnes doesn't emulate it properly due to using so many hacks, so the game will randomly lock up. Bsnes however, emulates most, if not all chips as accurately as possible, so games like Mario RPG will run perfectly. Snes9x isn't quite as accurate as Bsnes, but it's considered the second most accurate one. Your friend likely used Zsnes or something like it.