This is ingenious. It makes perfect sense. Mother's instincts notices something is different and wants to keep it from harming her other babies! But if they ALL smell different..."but I know these are my piglets"...then she must rely on her eyes...and then, the injured or different piglet doesn't get excluded.
It is an example of how God uses us, mankind, to tend to his creation. The creation is fallen, and in the wild that piglet would get excluded or killed. But when man follows God's wisdom in nature, harmony(though still fleeting) can be returned.
Permaculture sorta gets this work-towards-harmony, but sadly, usually tries to write God out of the equation. Little do people realize that God, in the Garden of Eden was creating the first culture of permanence(perma-culture) and the first sustainable agriculture (PERManent AgriCULTURE).
RE: IF ONLY ONE OF YOUR PIGLETS GOT HURT, WHY DID YOU PUT OINTMENT ON ALL OF THEM?