See, and I thought the story made it clear that the latter scenario was just a sort of flashback experience of Ennis', not the actual circumstances. See, this is why it should be obvious, it's too open to individual interpretation. How dare the the author and filmmakers make us think.
I googled the Wolf Creek thing and it's NOT a true story...damn those filmmakers, again. It's loosely - very loosely - based on an Aussie serial killer named Ivan Milat. So don't be fooled by those "based on actual events" claims. :nono