Castor saw Moon, or lunars brother. He remembered how moon always ignored lunar. Castor is very protective over lunar for some reason, no one really knew why. He probably told apollux but eh.

Castor walked to moon in pure anger. Castor pushed moon.

Castor:”I’ve wondered what the HELL was wrong with you for so damn long, then I found out you neglect lunar. The hell is wrong with you. I should just get rid of you.”

Castor could EASILY get rid of moon or anyone, as he was a star sign.