How can a union member be fired by another union member?
Did the word supervisor enter your consciousness at all when you read the story? The 7union part was just to let you know it was a union shop. The "union" supervisor was the supe that was in charge of the guy and the supe belonged to the union, that is how he could fire the guy, he was the boss.
Things have changed considerably. When I was an AFL-CIO member I was a “process tech” which was a fancy way of saying “foreman”. I had all the power of a company man while still paying union taxes.
I could have had anyone in my department fired at will. Fortunately I’m kinda sadistic and prefered to see them flee under their own power.