That was a moderately common thing in those days. In particular, iirc, there used to be a cable between the CD-ROM and the sound card that let you play audio off the CD without having the (limited) CPU needing to get involved, deal with audio encodings, etc. The CD would have a data track followed by a bunch of audio tracks, then the game can just say "Play track 5" and carry on with its business.
At least, that's my understanding. I was pretty young in those days and some of this is reconstructed "Oh, right, that would make sense".
The downside is that if you find a dump of only the data track/files it's hard to reconstruct the full experience of abandonware games. FireFight just isn't the same without the background music.