I know. But what? Exactly because of that. The last is what connects 699 chapters to the last one. She could be talking about the time she found out how Naruto was going to end (the movie has being made since 2 years ago, after all).
I look at it like this.
They were giving their thoughts/reactions to The Last.
Second if a movie is focusing heavily on one character (in this case Hinata) and their love life, it's going to be predictable. I mean if girl is in love with boy who doesn't pay much attention to her, but she continues to try to convey her feelings etc. I would expect them to end up together. The fact that Junko was shocked means that the movie isn't going to be predictable / have a predictable ending.
Sorry if this post is out of whack it's past 5AM, I should be sleeping.