Two head shots and the dog was still alive? What was the guy using, a Red Ryder?
The article only says pistol, which means it could very well be a .38, especially if one considers the hand strength of an 80 yo man. Even a .22.
One of the traits of the pit bull type dog is the “block-head” skull. So a head shot might not quite do it quickly.
PBs are tough sobs. I had one given to me. Chased a stud colt around a 30 acre pasture until the horse was almost give in. I finally caught it. Administered from a 12 gauge, a load of #4 buck shot point blank to its head. Half of its head was gone and the sob ran off and finally died.
We used crossed ones for hog dogs. They were the take down. Have seen them with their guts ripped out and never make a whimper when we sewed them up.