The point of that statement isn`t whether or not Noah ever existed (of course, you know that already, but bear with me). Jesus, being a child of his time (if he existed, that is, and said the things recoreded in the Gospels) being a child of his time, most probably believed that Noah existed, and that the flood was literal. But, his point is not to neither deny nor affirm his belief in Noah and the events of his day, but to use the "flood" as a parable to show how surprised and how unprepared people will be "when the son of man returns" etc. BUT:
The problem is that the JWs are so inconsistent it makes me wanna puke. Because they so freely and willingly use the view "oh its just a parable" on OTHER parts of the Bible, parts that do NOT fit their escathology, such as the parable of LAZARUS AND THE RICH MAN in Luke, 16. In fact, Jesus is using THIS parable in the EXACT same manner as he uses the "days of Noah" as a parable for how it will be when "the son of man" returns! BUT, this doesn`t suit the jws of course, so they just dismiss it as a "parable". But there is nothing in THIS parable EITHER (just as in the one about Noah) that would indicate that Jesus did NOT believe in a place of torment ("hell") in which the souls are conscious, and in the same manner, a HEAVEN, in which the souls are also conscious, as they are safe "in the bossom of Abraham".
Go figure.