Does saying "N*****" mean automatic ban?

To answer the title: yes Some context for you all, I was playing Blitz and my adc was pretty bad so I decided if we're going to win I might as well focus on roaming and having map pressure. All was well till the Lucian fed up with 2v1ing (he was getting solo exp was up 10 cs and 2 lvls) for awhile deiced to tower dive the enemy bot lane. I then "/mute all" and proceeded to do me. The game was dragging on with team mates playing TDM instead of actually trying to win I vent my frustration in chat(everyone muted still), thinking no one can see it, I spam the word "%%%%%%s" (now I know this probably wasn't the best of things for me to do and I realize now how serious Riot babysits their players, but we all do weird and sometimes questionable things when you think no one is watching or listening) but immediately after the game I was banned.

My problem with the ban is two things;

1. The mute system which the support team says that I can't see their text but they see mine, which I've never known ever to be the case(maybe it was changed and I never read about it in the patch notes)?. If they could see my text that would mean the "/mute all" is bugged or messed up.
2. The context in which the text is in, it is not directed towards anyone. I know it is a derogatory term but when people slip through your "player reviewed" tribunal system telling me that "my mom should have swallowed." Or " I hope some homeless guys fucks your sister after she falls asleep." its hard to look at what I said and say "You know what? I was wrong for saying these things and I promise myself to never do this again."

Idc if I get unbanned I just wanna know peoples thoughts on this situation and the tribunal system as a whole.