I'm almost ashamed to admit this, but my dad has done this with a couple rabid cats we had when I was little. I didn't ask questions, I was too young. But I did know what was going on.
He could never do anything like that now. One of my sister's GSD's was practically dead out in the kennel and he couldn't even bring himself to go get him to take him to the vet to be PTS. My brother had to do it.
As a side note: I also do not care for my father. I do not agree with his ways, on several different topics. So to me, that's just the way he WAS.
As others stated, we do not really know the entire story. And it is obviously a child who wrote it. Either way it is a very sad thing.
RIP Sadie. You did live a long life.