It was a pretty crude way to castrate. It was done that way a few hundred years back. I've heard that expression before. The first time was when I was really young. The tin snips were very sharp the and the turpentine sealed the wound by chemically burning the flesh. I'm pretty sure its what they did to some pigs when I was very young. I know the pigs made a lot of noise.
Well I'm not expert - the only thing I've ever read about castrating pigs was in some novel in high school where a guy's job was to tie the testicles off with string or twine and presumably after a while they fell off. Seemed pretty cringey to us all at the time.
I've heard they use elastic or rubber bands nowadays (at least for steer), but the family sold the dairy like 30 years ago so I've been out of the loop a while.