It's the logical conclusion because he differentiates between stone that is dead and stone that is not dead. You could argue that stone that is moving is still dead, but Zoro points out that the state of the stone Pica is in, is not dead. And if it's not dead, it's alive. He not only moves the golem, he can give the golem eyes and voice. Seems like fusing with stone and making it part of you.