How are you getting that from this story? They thought they had been discovered, and panicked. Pretty simple. Morality aside, staying quiet doesn't help your stealth if your enemy already has a flashlight pointed at you.
How could they have panicked? Surely this would've been a scenario that would've been planned for. I assume they would've trained for the crazy situation of encountering North Koreans in North Korea.
Retreat? This isn't a war, you can't just drop into another country and start killing people. At no point was it morally or legally justified to have engaged in combat in this situation. At the very least they need to verify it was a military target, and even then it's not justified.
