and canned it five days later, the bulletin said. The man heated the fish in a slow cooker overnight and then canned it, the bulletin said
FIVE days later.
Slow cooker is NOT hot enough no matter how long you heat it.
Botulism thrives in an oxygen-free environment. He heated it enough to cook the meat and seal the can but didn't have enough acid in the food to do it without a pressure canner. He was practically begging for this to happen.
Boil that shit, dude.
Edit: and don't eat it if it smells like that. Women and food, bro: don't eat it if it smells like that. Why do I even have to tell you?