"According to the boy, she does not eat chicken."
Translation:Secondo il ragazzo, lei non mangia pollo.
Duolingo can sometimes be inconsistent between different exercises. If in doubt, a definite article is more likely to be correct than not. That said, there are certain exceptions.
See the section 'When to use definite articles' here:
I answered correctly but lost a heart because it decided to randomly translate "boy" as "bambino". That word has not been introduced yet and how would a baby know a girl doesn't eat chicken, and why would we quote a baby as an authority on the eating habits of the girl? ...still love this app :) but I think randomly throwing in bambino was a glitch
I think it's because 'secondo' means "according to", whereas 'al ragazzo' means "to the boy" - but we can't use 'secondo al ragazzo' because that would translate as "according to to the boy", therefore 'secondo il ragazzo' is correct as it translates to "according to (secondo) the (il) boy (ragazzo)". At least, that's what I've tried to work out ...