That was just an interaction with killingham. Just like sanji vs king.
Zoro and Killingham aren't even close to eachother. He's beside Sommers though.
And Sanji always fights on behalf of the other strawhats. So this follows the usual pattern.
Sanji vs Kuroobi cause he insulted Nami
Sanji vs Mr.2 for Usopps goggles
Sanji vs Jyabura to save Usopp
Sanji vs Absalom to save Nami
Sanji vs Queen to save Chopper
Sanji vs Killingham cause he insulted Jinbe
Unless you want:
Sanji vs Sommers to save Zoro