Most likely it was meant for tawerns that usually appear in Ancaria. But due to an unknown reason, you can't actually hear this tune while you meet those buildings. Instead you have the same track that you have heard outside. Maybe it's just a bug in form of broken trigger, but we don't know it for sure.
In fact, this is just plain accordion melody, with usual pub SFXs on the foreground (burps, bottle's chiming, sounds of drinking alcohol, etc.)
The name of the file is "music_pub.mp3".
Since the Linux version is just the emulated Windows 32 version, you will also have the same track in /mp3 root. Due to the same reason you will have this tune in patched version with Sacred Underworld (W32) expansion.