I only discovered very recently that it was supposed to have music as well. I played on Windows XP back in the day, and I'm 99% sure the music must have been turned off by default.

Definitely did - that MIDI file is etched into everyone's soul who played Space Cadet but this was early days, maybe it's possible the win9x machine you played on didn't have a sound card?

EDIT: From what others have said it sounds like it's off by default. It's been decades so I don't remember.

Apparently it did, but it was turned off by default since it could have a performance impact on slower machines.

Yes. It's original.