If he was assisted, it wasn't by humans. He was hatched in a nest. One of two that hatched and were found trampled against a wall. I assumed his problems were due to the trampling, but I called times up on the remaining eggs and the one that I looked inside had what looked like a prematurely internally pipped duckling - with legs that didn't look quite the same size.
Is there something in the incubation process that could do this? I don't think that egg and the one gimpy duckling hatched from were from the same duck.
Here's a picture of him. You can see how the wing points forward like an arm. Totally adorable how human-like it makes him seem when he leans on his water dish with his arm over the edge - but not terribly functional.
View attachment 3169782.
I take back what I said about the leg being totally limp, though. When I was trying to get a picture, he totally used the top of his foot to launch himself out of view.