According to Mashable, getting a dozen double yolks is an almost statistically impossibility. Using their math, getting even six in a row is a one in a quintillion chance.
Turns out, it's not really such a mystery. Sauders sells double-yolked eggs by the dozen.
So this was just a packaging error where the double-yolkers that had been identified and separated for the double-yolk package got inserted into a normal carton by mistake.