'Devadatta is fat and he does not eat during the day; therefore, Devadatta eats during the night.' In classical Indian logic, this is a case of

The night-eating conclusion is reached by arthapatti, postulation.

A given fact (Devadatta is fat yet fasts by day) cannot stand on its own.

To reconcile the fatness with the daytime fast we must postulate night-eating.

The extra fact is assumed because it alone explains the given ones.

Such necessary presumption to remove an apparent conflict is arthapatti.