Help me understand this behavior

Hi guys!

I have two baby turtles (western painted) which are more less 8 months old.

Initially they were together but 2 month after I saw aggression of one turtles (slightly bigger) towards the other.

I've since bought a big tank and split it in half for the safety of both turtles.

Until now they have lived completely fine on their own side of the tank, never acknowledging eachother as far as I've noticed. Their routines are normal, they bask a lot and eat a lot.

But just today I notice that the turtle that was the previously aggressive was doing the jazz hands to the other through their partition.

What does this behavior mean? I attached a video of that for reference.

I'm curious which one of them feels intimidated and if could be related to any mating behavior, tho they are very young.

Thank you guys!

P.S. the water level is low cause I'm doing a water change at the moment.