This was well worth the wait. You guessed correctly. It was a boss, it was actually the final boss of the game. And as the fight actually progresses(indicated by the music), you can see the environment changing. To the point where on the last segment, there's a legitimate stage in the background. I honestly like to envision this fight as it literally being rock vs classic rather than EDM. Given how it keeps switching back to classical in the base version of the song. This is also the only song to not have any separate rock track to its base track. Every other boss(minus the rap boss) in the game has a base track, rock track, and EDM track. Granted every other song doesn't really have rock in their base tracks at all so it makes sense.
I actually have played through the game and for the most part it was fun. But you really need to have a sense of rhythm for the battles because otherwise you will not have a fun time. The enemies attack with the beat and some attacks(usually marked by a different color) can be reflected if you hit with the beat. Also the DK West battles are fundamentally different and start out alright... but holy hell whoever made the last one was on a Dark Souls binge and made it to be absurdly difficult.