One of the young people I used to work with would only eat twiglets dipped in marmite, morning noon and night.Again not saying Atticus is autistic but the whole incredibly limited food thing is an absolutely classic autistic trait.
Lots of autistic children and adults will have very limited taste with food. I've heard of children who will only eat beige coloured food for example, or foods of certain colours, very bland and safe choices and don't like anything unusual or what they might perceive as strange combinations.