Because those moods are defined as varying states of the chemicals in the saline solution.
Defining the moods that way seems wrong. If some alien species evolves with a distinct biochemistry that has some similar moods, we wouldn't assert that they weren't the same. Rather the moods correspond to varying chemical states in these bags of saline solution and they are varying chemical states that predict some macroscopic behaviors of those saline solution containers, such as their tendencies to damage other containers or engage in activities that produce new containers.
Here's the new thread for posting quotes, with the usual rules: