OKay, the Finger sign doesn't have a significant meaning. Squall looked at her, she noticed, shook her finger and got him to dance.

Likely because she wanted to, and it looked like he had a momentary interest in her, so she decided to dance with him.

Why would that be his flashback? Because that was the first time they met. It's very common to use something like that for a flashback.

As for the last scene? Again another common use of repetition, recreating something that resembles their first meeting. This repetition of events is used to signify the importance of Squall and Rinoa meeting.

It's a story telling device, not a sign of anything.

Though you pointing this out does make me think they put a bit more effort into their story then I originally thought.

Even if it was still a bit of a mess.