He might be using Arch or Gentoo, or another of the more "DIY" oriented distros. Last time I used Gentoo you still had to really go out of your way to install pulseaudio, though that was four years ago so I don't know if that has changed.
I'm using Arch, but this applies to any distro if you don't use a DM and instead use xinit.
I much much prefer the simplicity of only using what I at least partially understand - the more magic (ie a DM) the more shit to go wrong that you don't understand.
It is the default in all mayor DEs, but he might have a custom X session, using a standalone window manager and extra tools. Or he could work in the console.
