the movie will have a flashback of Kakashi from the time he was 17 and in the ANBU, it won't be about him or even have anything involved with his flashback, they're just saying it to get public attention from the crappy tournament plot.

my bet is that the flashback will be something like this:
"a tournament in the snow country? i remember when i was back in the ANBU, i went there once {insert Kakashi in age seventeen with anbu uniform}, but i never thought i'll go back there again!"

and that will be the end of it...