You shouldn't think of this paper as being in English. You should think of it as being written in Science.

Science != Pure Mathematics.

They proved that THERE EXIST children who are not sensitive to these agents. 5% may be enough.

Yes, you can “prove” very little outside pure mathematics. But “doesn't prove” doesn't imply “doesn't support”. Chapter 1 of Probability Theory by E. T. Jaynes makes that clear.

(And BTW, how comes you're taking “school-age children” to mean “all school-age children” but you're not taking “artificial food colorings” to mean ‘all artificial food colorings’?)