But there's nothing in the episode to indicate the Gorn have any of that (except their own POV, which every even vaguely sentient critter has). Kirk gives the benefit of the doubt to a being he knows bupkis about. And then he shows mercy. *That's* what impressed the Metron. The two don't necessarily follow each other - Kirk could've thought "might've had their reasons" and still chose to kill the Gorn. It was his choice not to kill a helpless enemy - an enemy the Metron says would've killed him.The story of the Gorn being thoughtful, having their own point-of-view, and taking actions that can be understandable. As Kirk came to realize at the end of "Arena" and thus the reason why the Metrons chose to spare him.
Once more:
METRON: By sparing your helpless enemy who surely would have destroyed you, you demonstrated the advanced trait of mercy, something we hardly expected.
THANK YOU! Yes, this.Kirk's epiphany is still in the future. So is the potential for peace that Spock and McCoy implied might be possible through diplomacy. We're still in the part of the story where the Gorn are monsters.
Now, the problem with Kirk not having heard of the Gorn in "Arena"? Honestly, I'm putting that with "Vulcania" and "no women starship captains" in the Things I'm Ignoring In TOS box.