If you thought that was NEAT, look for YEAHYEAHYEAH in the same file. I thought it might actually be code in an unrolled loop that looks NEAT on accident. But no it's invalid 68k code, and the existence of both YEAH and NEAT suggests those are meant to be strings.

I worked on a Halloween themed album sold on cartridge, called Heebie-GBs 2014, and included this feature to play an evil laugh in the background of the title screen. I imagined that someone would hear this, and then conclude that their Gameboy was haunted!

Late reply since I don't check bsky so often. But I'll also point out that the same "hack" can even be used to play sampled audio, by essentially producing voltage levels with modulated PWM.