It seems that it was done as an adventure example that is as short as possible, although it is still a true adventure hook, but it is no longer available on its website.
The synopsis is basically:
There is an orc, he has a cake, the adventurers are hungry.
It has everything an adventure needs: an adversity, a McGuffin that the players need and a reason to get it.
Somehow this caught on and more people started using "Orc & Pie" as a phrase to mean "extremely simplistic adventure".