With a typical data disc, a single "track" is written, containing all the files and folders clumped together.
With an audio disc, multiple tracks are written, none of them containing any files - each track contains the wave-form data for a single track of music.
Many older game discs (eg PSX games) make use of a mixture of the two techniques: first a data track is written containing all the game files, and then the following tracks are written as on any audio CD. In short, you can take such a disc, stick it in a ye-olde CD player, and it'll be able to play everything but the first track (which isn't music).
Ripped copies of games are notorious for replacing the audio tracks with much shorter (or empty) versions. These compress down for easy online distribution. The practise is much less common in the modern age where pretty much anything can be thrown over the internet in next to no time.
Although Windows Explorer won't show you this extra audio content, odds are if you right click the disc there you'll get a Play option on the context menu. iTunes or whatever should be able to handle it, if you're really not sure you're looking in the right place.
I'd just like to note that autoplay will start playing the audio on the TFTD PSX disc, but the files played are the ones I mentioned in my previous post: ABOVESEQ, BELOWSEQ, FLIC, GEOSEQ & XCOMPAL. The music isn't.
I did look up STR and it seems those are PSX video files, not music.