It's how the system is programmed. Someone reports you, the system is supposed to flash a warning at you. If you didn't actually do anything, you won't be punished for it. Yes, the false reports are unsettling. But eventually, you learn to let it go. Heck, I have been reported so many times for "offensive language" in games where I've never typed in a single word that I've lost count. I've yet to get a single warning from Riot and I've even gone so far as to submit a support ticket asking if I am in danger during one day of heavy pop ups. I was assured I was fine.
The vindication is knowing that someone with a history of wasting Riot's time with false reports is eventually ignored. I imagine a Riot employee at his desk and seeing a familiar name having submitted another report ticket and saying "Oh, look. THAT person again. Dee-leet-ted." Whether it was real or not.
Crying "wolf" too many times has consequences.