To be clear, when a developer submits a finished game for publication, it's supposed to reveal all of its cheat codes, but this particular one was never disclosed for the simple reason that Sony would've undoubtedly kicked it back to development for removal. Apparently, Piper isn't too worried about letting his secret out into the wild more than two decades later.
There's a bunch of debug/dev features hidden in production software that I stay quiet with from companies i worked for. Revealing them would probably make me unemployable. Or worse, slapped with a lawsuit.
So I'm glad this guy was probably retiring or switching careers.