"Dismissed the service" presumably means taken off Royal duties. Quite right, too, and he deserves a bit more of a reprimand from his Commanding Officer.
I doubt he has been thrown out of the army, it would say discharged from the service if he had. Fired just means relieved of this particular job. He will rejoin his regiment and not be allowed palace guard duty again.
I know really nothing about the British Army, or any for that matter; but, I think that Obiter could be correct in the respect that he is entitled to a hearing (court marshall?). After all, isn't that the tradition?