The Chofetz Chaim introduces the 8th chapter with the caveat that anything that sounds simple has to be brought up anyways either because it fits better in the flow or because needs reminders and reiteration so that they won’t make mistakes, in any event their is usually something new that comes out in the end. He begins the chapter with saying that speaking lashon hara applies to both men and women even with relatives and even if you are talking about relatives and they don’t care what you say because we’re all family still it’s lashon hara because you might’ve come to conclusions to quick. This happens to be true about lashon hara on the topic of things done between man and his fellow man, where you can’t come to conclusions you have to question and prove first. But if you saw something wrong being done between man and Hashem then even if you did come to the right conclusion you can’t say it to anyone else because there is no purpose unless you think this is the only way to correct his folly by having someone else go over to him and help him.
The Chofetz Chaim in his Be’er Mayim Chaim explains that this halacha is based on the episodes of Yosef and his brothers as well as Miriam talking to Aharon about Moshe. The Sifri says that when Miriam told Aharon about Moshe separating from his wife the purpose was to go over to him and rebuke him. She even praised Moshe granting that he was a greater prophet than them but is he holier than our forefathers who had prophecy and stayed married. She did this for the sake of the mitzvah of having children, totally pure intentions, yet she was punished. Why was she punished? Because she came to conclusions to quickly. Her attitude should not have been Moshe is wrong and we have to rebuke him rather it should have been something doesn’t look right why don’t we ask him what’s wrong and clarify the issue. A change of perspective and attitude could be the difference of Whether it’s lashon hara or not. Also, even though Moshe Rabbeinu didn’t care one iota what was said because he is so humble, he wasn’t insulted in any way, still it is lashon hara.