Well I'd say try not to see it as a rule set in stone, you don't have to imitate it exactly and fear that if you do it differently you're doing something wrong. Each scene you light will have different sorts of challenges, so take what you see as a guide more than anything. You can use an HDRI only or you can mix it with a sun lamp, it's all up to you and your judgment when it comes to lighting, it's all eye and discernment if you ask me.
