No, you don't have to be smart to cook. I don't know if you even have to be smart to cook
well. I suspect not, because I learned to cook good food pretty quickly; someone who was even dumber than I am might take a little longer, but it still wouldn't be a substantial fraction of a human lifespan.
It does take work, but not a huge amount of work, especially if the aim is to feed your family, not to cook well. Oranges and bananas, you don't even have to cook. A peanut-butter sandwich is two minutes if you already have bread and peanut butter. Cooking brown rice or lentils involves dumping a measuring cup into a pot three or four times and setting a timer. Same thing's true of eggs, oatmeal, polenta, ramen, and grits. Other beans, you have to dump into a pot of water the night before, and you probably ought to sort them so you don't bite a rock, which might take five or ten minutes for a big pot. A big pot of beans and a big pot of rice can satisfy the caloric and protein needs of a family of four for a few days.
And if you dump garlic, onions, butter, soy sauce, salt, pepper, mayonnaise, and hot sauce on any random barely-edible non-sweet crap, you can get it up to the level of McDonald's or Popeye's pretty quick.
There are some cheap foods that require a lot of work. Collards are a pain. Baking your own bread may be cheaper than buying it in a store‚ but it's a lot of work. And about any vegetable you use in a dish is gonna need some slicing. But it doesn't require you to be "industrious" at the level of digging a ditch for eight hours, or working overtime at the bubblebath factory they can't afford to heat.
Now, it's true you aren't born knowing this stuff. You have to learn it, and even if you know it in theory you may not be in the habit of putting it into practice. The soft-drink aisle and the potato chips are pretty tempting. Stopping in at McDonald's on the way home from school is a lot more immediate than stopping at Jewel Osco for a loaf of bread and some peanut butter, even if you evade the peanut butter. And if you've just gotten off your split shift at the call center and you have a couple of kids to feed before you start in on your homework, it's pretty hard to motivate yourself to cook. I'm not trying to minimize the difficulty of being poor in the US.
I'm just saying the problem with food is not that good food is out of reach.