The article is not claiming that food colouring causes neurodiverdancy. The summary of the article states:

Excluding artificial food colors from children’s diets can improve ADHD symptoms.

It then goes on to explain that food colouring can affect the behaviour of young children, including those with ADHD.

This time, researchers found that artificial colors and other food additives in processed foods appeared to exacerbate hyperactive behaviors—inattention, impulsivity, and overactivity—among young children, with more pronounced effects in three-year-olds relative to eight-or nine-year-olds.

But what happens in children already diagnosed with ADHD if you remove artificial food colors? In a meta-analysis of randomized controlled trials for dietary interventions for ADHD, excluding artificial food colors from the diet significantly improved behavior.