That schema was popular for a while. That weird format was probably Windows Media Audio (wma).The audio data was still there and was accessible with the right software/firmware combo. But sometimes those disks would auto run and inject malware. This was usually the Sony root kit. Sometimes that malware would disable your system's ability to access the audio tracks. Because for way too long windows machines would autoplay anything that was plugged into it and EVERYTHING ran as administrator. Most CD drives back then had firmware that could play the CD audio directly from the drive to your speakers, bypassing the OS entirely, so most people would never notice a difference until they tried to rip the tracks themselves.

Some older games worked this way too, without the malware. The software would be on the data portion and instead of copying big wave file to your PC (because mp3s weren't really a popular thing yet and drive speeds were slow), they would just play the audio from the audio track portion of the disk. You could sometimes pop those disks into a dumb CD player and listen to the audio directly as long as you skipped the data track at the beginning. You could burn your own disks like this around the same time. I remember making a few mixtapes on CD that stored a CD label/envelope tracklist as a PDF and mp3s of the CD tracks themselves on a data track at the end. Putting the data at the end allowed you to play it in a dumb CD player without having to skip the data track.