I am only a learner myself, but my guess is that it is because the Irish question uses "toradh" which means "a (single) fruit," but in English if you say "is there fruit in front of you," the amount is ambiguous.* There could be one single fruit, or a whole basket of fruit, since "fruit" can function as a plural without having to add "s." If asked to translate "is there fruit in front of you" from English to Irish my instinct would be to answer with "an bhfuil torthaí romhat."
*Or am I incorrect, since "is" is the 3rd person singular form of "to be."
"An" in this sentence is not the article "the", but rather a question marker. So the lack of a definite article "the" in the original is the (frustrating) reason this is flagged as an error in sentences like this.
"An bhfuil an toradh romhat?" = closer to " Is the fruit in front of you?".