In (American) English "the fruit" is both singular and plural-- "the fruits" is almost never used outside archaic/idiomatic speech (e.g., "the fruits of their labor") -- would the program have accepted "I eat the fruit" as an alternative? (To explicitly specify that fruit is plural, we generally have to add a phrase like "several pieces of"-- would that have been accepted?)
It would be exceedingly rare in English to say, "I eat the fruits", fruit being a collective noun like people, beer, or deer. "I see the peoples" would be quite different than "I see the people". I rarely drink beers, as I prefer to stick with one type of beer. I can't even think of a situation where "deers" would be appropriate, unless one is speaking of different species of deer, but even then it seems very odd.
Local idiom (in southern Ontario), understands "I eat the fruits" as "I eat the homosexuals", which a bit pejorative. And cannibalistic.