Other mistake: In this episode, when Kirk's phaser was on overload, it made a small explosion, but in "The Conscience of the King", a phaser on overload would destroy 2-3 decks of the Enterprise.
Other mistake: After Kirk makes the cairn of rocks to bury D'Amato, he places a rock with the man's name on it. If the phasers couldn't cut the rocks of the planet, how did he cut a squared rectangular rock, and how did he put D'Amato's name on it?
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.