I was going to say you're right—that's odd, because I hadn't heard or seen that before—only that they turn in circles before lying down. As it turns out, you can google either phrase and find myriad speculations as to why, from magnetic orientation to getting their nose into the wind (for defensive advantage) to hardwired holdovers from prehistoric times, to stomping down grass/snow, etc.


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From observing dogs all my life, I tend to agree with the defensive position/fight or flight response theory. In both situations (pooping and lying down) dogs are at a defensive disadvantage—vulnerable to attack by predators/competitors. Dogs who can sense (smell) danger/trouble coming have just that slightest edge in defending themselves and/or staying alive in order to perpetuate the species.

Doc