being banned for something but the other 3 people weren't

So, I have a friend who recently got banned or i guess it would suspended w/e, we just started playing together recently, and he is usually pretty chill, but this premade group of 3 were bagging on him really hard all game. He said the magical 3 letters and got hit with the ban, I sent a friend request to the guys who said that to him, to my surprise they accepted and I asked if I could join acting like I was also flaming him or whatever, got them on my friends list (mind you me and my friend did also report them for saying those 3 magic letters.) so a couple days pass and I still see them getting on and still playing, how is it that, my friend can get banned for this but 3 other people who also said the same thing to him don't? To me feels like there is some kind of flaw in system, and I think it's just unfair, and I'm sure there will be some that say "well life is unfair" or something like that, but if one person is going be punished for something then everybody needs to be punished for the same crime, just kind of annoyed because this is the one game me and my bud can play together, and feels like something unjust is going for punishment not to be distributed equally.