Different translations take different views of this verse. Probably the most extreme is the Bible in Basic English which translates it,
(Pro 10:18 BBE) Hate is covered up by the lips of the upright man, but he who lets out evil about another is foolish.That makes what is literally “lying” (8267) “lips” (8193) into a virtue. Somehow I don’t think that is the intent of Solomon.
Wesley had an interesting explanation. He thought this was talking about flattery. When you think about it, flattery can be a lie. It can also be the truth, your call.
So? Hatred is something we have some control over. Being open about it might spur us to do something about it.