What does 2 Samuel 4:10 mean?

'When someone came to me at Ziklag and thought he was bringing good news by saying, 'Saul is dead,' I grabbed him and killed him. That was the reward I gave him for his news.' 2 Samuel 4:10 - Modern Text Bible

(David reminds them that he doesn't reward people for killing Saul or his family. He executed the last person who thought he was doing David a favor by killing Saul.)