One of the things my wife will attest to is that when I get a craving it is specific and nothing else will do. It isn't that I'm a picky eater, overall, but that I am struck by cravings. There are days when some foods aren't appealing, too.
Parents and teachers tell me that some children and teens with autism are much, much pickier. One mother told me her autistic son went through a period when he would only eat the "blue box" of macaroni and cheese for lunch. Nothing else was acceptable for the young boy. When the mother tried to add anything to the pasta, he wouldn't touch it.
A diet of cheese and pasta? I can foresee a weight issue if the boy isn't active enough. Maybe a multi-vitamin would help, but how does anyone get a balanced nutritional intake from Kraft instant Mac n' Cheese?
I'm wondering if all children don't go through food stages. My wife says she did. I've seen this among the children of friends and coworkers, too. Some children won't eat vegetables, others won't touch pudding. Seriously, how can anyone not love pudding? Especially tapioca or dark chocolate. (I also love the seasonal special flavors, like pumpkin spice pudding and peppermint chip.)
Schools don't have many choices at lunch. You get what they have or nothing. How does an autistic child deal with this? I'd eat most things in the cafeteria. I volunteered for cafeteria duty because you could have extra of some things, like the "shoe fly bread" or whatever it was called. I have to admit, I even liked the deep-fried beef and bean burritos. I didn't care for what they called "pizza" though. It wasn't pizza.
At least as an adult I can choose my meals. Today, we had pizza for lunch. The lunch was under 300 calories, too. But, I wasn't that impressed with the pizza crust. I believe it was made in the same factory that must provide the school lunch pizzas.