That part of the video certainly looks like communication. I recognize the head bobbing behavior, that was a common thing I saw in my cuttles too. The tentacle play behaviors of the one on the right look like some of the courtship behaviors, but in this case it looks like maybe unrequited love.
I wish I knew how to prevent male male aggression or to sex the animal prior to that point.
By this stage, I had my cuttles occupying the full volume of a 29 gal tank. So the death wasnt instant, they chased each other and fought for a day or two before I decided it was going too far. By that point it was too late, the weaker had been injured and died of his injuries after I removed him.
So my only thought is next time, to remove any cuttlefish that start getting picked on at the first sign of aggression. Which means setting up yet another cuttlefish tank, as if the first one wasnt enough work