Those birds can dive through the ice to get fish if the ice is shallow enough. My guess is that the bird dove through, but he couldn't find the hole out and found that hole instead or he ate the fish that had the line in him and then the fishermen pulled him out.
He caught a ******* loon, holy **** . I didn't even know those things could break through the ice! I just assumed the little ***** hibernated for the winter or something.