Question answering (QA) vs Chatbots
Question-answering (QA) is sometimes used to refer to the task where the input to the system is a question and a list of possible answers (normally only a handful) or a paragraph where the answer is supposed to be found, and the expected answer is the index of the correct answer or the start/end positions where the answer located within the text.

In chatbots, the task is normally defined more generically as "answer the given question". This can be approached in many ways, like with chit chat chatbots, where you simply train your system with pairs of question and answer much like a machine translation system, or with information retrieval chatbots, which make use of documents to identify the relevant pieces of composes the answer based on them.

Therefore, in the usual QA definition, QA is much more constrained (i.e. easier) than chatbots.