I think China is building military capability because they think they need it. We don’t know why. If you think about the game theoretic aspects of this, then it makes sense for the US to preemptively mass forces nearby even if they believe China’s ambitions are peaceful. You can’t just assume that because your opponent is telling you that. And vice-versa if you’re China and you see the US massing forces.
The fact that Chinese fishing ships invade other territorial waters to steal fish and damage habitat and the fact that the premier wants to bring Taiwan back suggests a will to be the aggressor.