In a previous life, I picked up quite a bit of experience running a number of restaurants.
You cannot put 10 gallons of hot anything into refrigeration and expect that to be safe or sanitary. You either have to keep it covered on the fire or divide it up into smaller containers for cooling in the fridge. Bottom line is that if you are going to refrigerate something, you need to get it cooled down to 40°F as fast as possible.
If you would have split the batch into four parts (2 1/2 gal ea), and then placed into commercial refrigeration, you would have been fine. You cannot use a household fridge in this case though because it doesn't have the cooling power with that much heat placed inside all at once.
Although I will admit, proper process or not, I am surprised that 10 gal of Gumbo went bad that quick. I've made similar mistakes over the years without that level of spoilage occurring.