Facebook redefined chatbots almost overnight by permitting bots on Messenger. Up to that point the consensus was emerging that chatbots were actually what had been previously known as chatterbots. Originally, “chat bots” were any bots on Internet Relay Chat (IRC); but, today any bot, or automation, on any chat channel may be termed chatbot. Thus a grand confusion has emerged in that there is an expectation that bots on chat channels should be natural language dialog systems.
Up to this point, most chatbots (aka chatterbots) have been pattern matching systems, see all Loebner Prize contestants for examples. Whereas, question answering systems generally use different technology, such as machine learning based on question-answer pairs. Additionally, chatterbots have a general conversational ability, for instance personality based common sense knowledge, that often domain focused question answering systems do not have.