Grandpa's sayings, "You will eat a peck of dirt before you die"
At the supermarket check outs there are those little magazines about most everything. I picked up one about the benefits of Apple Cider and found a few pages telling about the benefits of a few spoonfulls if one thinks they may have eaten bad food. THEY claim that the acidity will kill most food derived illnesses.
First Holiday in Tenn. my MIL cooked up a storm, turkey, ham all the fixins. After the meal with the dishes and utensils removed she left all the food on the table and threw a sheet over it. No refrigeration for anything.
For the next 2 days everyone ate that food, except for me, Heck I like to starved to death amid all that bounty. Got to realise this was a farm, people tracking in chicken, cow and goat poo on the bottom of their feet. People coming and going, coughing and sneezing, The food was uncovered for 6 or more hours a day as people need to eat.
No one got ill from the food, only problem was me as I was about to fight the rabbits for their bunny food.
It must take allot of foul ups before food becomes contaminated enough to make people ill. Like a chain reaction, starting at the producers, then the method of transportation to the stores, say a freezer truck breaks down and the product begins to thaw out. Then at the store, pallets left on a loading dock in very hot weather, then into the stores coolers that may have a problem keeping the temperature at the correct level.
Home to a kitchen where the refrigerate may be an older model and without your knowledge the neighbors roaches have just found your house. The trip home in a hot car or even one airconditioned takes 30 minutes. You carry in your bags of food and the phone rings, someone is at the front door. After another 30 minutes finally you put away your food that you will serve to the family that has been frozen and partially defrosted 6-7 times. At this point perhaps the cats or roaches have climbed all over your counters, gotten into the utensil draws.
It takes a massive amount of screw ups to cause food poisoning, in the case of your son, I would not worry too much, true he did mix and match cooked chicken with the raw stuff, he knows better now.
I would be more worried about a street vender or a pot luck Church dinner, we survive them with no problem.