Retaining the juices in the meat has to do with the temperature at which the meat is cut. Resting allows the temperature to drop, which creates less pressure, so the juices aren't forced out of the meat nearly as strongly.
The title is click-bait. The major rule is correct, not wrong. But, now we know a little bit more about why this rule works.
> As the meat rests (and therefore cools) that vapor pressure decreases, and so does the juice loss. It's not about reabsorption or thickening as the juices cool, which is another common explanation that's been offered over the years. It's simply about pressure. Control for final internal temperature, and—rested or not—the juice loss is the same.