My friend was banned for no reason?

So obviously as it says in the title, my friend was banned from playing in Arams. He's never left a game early, doesn't really talk in chat so there wouldn't be any reason why he would get banned for toxic behavior. He's new to the game, thus why he has been playing aram's to get used to playing. He played a couple of games yesterday, and then came home today to find out that he has been banned. He has received no email telling him the reason for being banned and there's no real way to dispute or ask anyone as to why he has been banned.

As someone who has been playing this game myself for 4-5 years now, I've never seen this happen to a nicer person. So, I'm not sure if there's anyone here who could give me some information to help him out at all, but if by chance a moderator could just help me out a little bit that would be appreciated. Kinda bummed that toxic players/people who afk all the time aren't getting banned, but someone who hasn't done anything gets a perma ban?