Because the plasma lifeform has been watching over him all the time, and because the head of state already knows the truth, Alex knows that all the details of the implementation of the comet deterrence plan will be kept strictly confidential to him. This is not the same as building a lunar base. Every progress and every detail of the lunar base construction plan will be discussed with Alex, which is exactly the opposite of the comet deterrence plan.
Therefore, Alex knew everything about the construction of the lunar base, but he knew nothing about the implementation of the comet deterrence plan. Alex didn't even know whether the paper tiger he sent out was taken away by the head of state, or whether the head of state thought about the information he wanted to tell human civilization from the paper tiger.