To your point about drafting - sometimes in keirins, people go uptrack a little bit to ensure that they have a good line forward. It's called "keeping your front wheel clean." Since I'm not much of a sprinter I rely on the opposite tactic - coming from behind and boxing in a rider behind whoever's in front of him.
Anyway, I'm not sure if the riders you saw were defending their positions and trying to keep their front wheels clean, but it's something to think about.
As for that flick - common tactic, and like carleton says, potentially illegal. Also, note that if you're in a position to do it, you're sprinting full gas and you are running out of steam and afraid that somebody else is gonna come around you. If you try and flick right to the red line, know that it's so, so, so easy to overshoot. Be careful. You don't want to flick yourself into somebody.