They don't encounter people like you very often. I don't know if you were a return visit or if this was their first time there, but JWs are typically ill-prepared to speak to people who've done their research. I wouldn't expect them to return. They were probably caught off guard and resorted to reciting talking points they were comfortable with regardless of the topic.
It's good that they were forced to confront an inconsistency in their beliefs (the end-is-near stuff). It probably made them uncomfortable having to lie to you that way. It may not bear fruit immediately, but it was a series of these types of confrontations that led me to loose my zeal for field service. Years later I quit the religion altogether.