Did an Admiral failed to take DR out of a giant?
Xebec literally hard fought killing his own kin DR who is far not stronger than Dr Giants.
Not even changing them back to human, He killed them. ( especially implying with what he said )
Xebec kill an Admiral.
Zoro tried to killed them but failed, while Chopper didn't killed them.
Chopper literally had something that even Xebec failed to do to his own kin.
Its not that hard to not put two on two together lol