It's very possible for male Bettas to hop from side to side for fight
and then flip back over into his own side.
This is main reason I don't keep divided male Betta tanks. I keep them
in either 1g's, 2 1/2g's, or 3g's by themsleves.
The females I keep in my 75g with my Angelfish.
I've seen Bettas jump through the smallest of openings.
It's amazing how good their aim is when flopping out of the water,
through a hole or wriggling through a space to have either a fight or
to spawn, and then find their way back again.