What is a safe food? How could a macdonald become one of these? A safe food must be something that they have initally been given by their parents?
When a child has food issues and the list of what they will eat dwindles - if there was even anything on the list to begin with - you try all sorts of different foods from all sorts of different sources. For some parents this will include processed foods and fast food because when you're worried and desperate you try every option.
DS was on milk only until around 8 or 9 months of age because everything offered was rejected after the initial first taste. By the time he was 18 months old he would only eat mushed up Weetabix, bananas, sweetcorn, and yoghurt. With many years of work he now, aged almost 7, eats Weetabix, peanut butter sandwiches (smooth only, white bread only), plain chicken, chicken dippers, plain pasta, plain baked potato, cucumber, and sweetcorn and that's it. He will very occasionally tolerate a Yorkshire pudding or some green pepper. He takes daily vitamin supplements and has milk to up his calories but is underweight for his age, he's on the 2nd centile for weight and 50th for height. His three year old sibling recently overtook him in weight by a whole 1lb.
As well as the restrictions on what he eats he also has rules around food such as foods can't touch, they have to be served at room temperature as he won't eat anything hot, no sauce, no flavourings or seasoning, specific plate, specific cutlery, and so on.
It is worrying, tiring, and you don't know how hard it is until you've been through it. He will literally go days without food if there is nothing acceptable to eat. If a parent has a child with food issues but that child will eat McDonalds then of course they're going to offer it.