The way the program works doesn't literally involve any type of computer logic / artificial intelligence. There is a list of correct / accepted answers for each question which is input by a human. It is easy for a human to not consider all of the many possible correct answers ... that is why the users are asked to make suggestion such as "My answer should have been accepted." Periodically someone from the Duo staff reviews the suggestions and makes additions to the data base. I have read that some questions have over 100 accepted answers.
Sallyann_54: In Duolingo you have to sort of invent or make up a story for the sentences to make sense. In this case, I imagine somebody asking about the order in which a group of people are going to do something. The first person asks (about John) "Does he go first?", the next person answers, "No, he follows".
It is more likely that an English speaker would say this sentence with an object, such as, "No, he is following us." Or we might also say, "No, he is following along," however, with a different meaning.
In any case, I am doubtful you would hear, "No, he follows," without some sort of additional information in typical North American conversation, perhaps in Britain?
It is wrong. My english is bad, I'm sorry. "He doesn't follow" is "el no sigue" but "No, el sigue" is "No, he follow". The two sentences have different meanings. The first sentence says for example that he does not follow his cat, this is a negative sentence. But the second sentence is a positive sentence: "he follow his cat". I hope you understand me.