Bannable offense or not?

(Keep in mind this is a ranked game, and I am in my promo series 1/1 , so this is important, and I even tell my team that in champ select)

So, this thread isn't about me, but is about another player I recently played a game with. So, to keep things simple, I am amumu, and he is Renekton. So, as the game progresses, I am ganking lanes a lot, right, since thats just Amumu things, and slowly, this Renekton starts snowballing like crazy on Irelia, right. So, things are looking all good, but unfortunately, our mid lane is just getting destroyed, and their Diana ends up crazy fed. However, fortunately, our Corki and Bard bot lane is doing amazing, and they get fed. So, basically, Diana is fed on their team, and Renekton, Corki, and I are fed on my team. So basically, after a while, we are just doing some objectives and stuff, getting towers, and randomly, this Renekton just starts semi trolling. And by that, I mean he is just standing there in lane, just afk farming, and is staying in my jungle taking all my camps. When our team asks "Yo renek group for baron", or "Hey renek lets group and end", he just replies "if you guys try, you can win by yourself", and returns to farming. And this is just the start of it, so later, when 4 of us are there at elder dragon fighting with 5 people on the other team, he is just sitting at the opposite teams inhibitor tower dancing, and doesnt move. In fact, it seems like he doesnt even care. He is just there dancing. Fortunately, Corki and I are fed enough to win the fight, but then, their irelia comes in for cleanup and kills corki. I manage to get away with around 100 health. This entire time, renek is still top dancing. In fact, he doesnt leave until around 50 seconds later, when the enemy team's death timers are up.

Overall, this Renekton probably spent around 20 minutes doing this, just farming my jungle, and not grouping or responding to anything we tell him to do. So, I say in all chat, "Can we please report this renekton for not cooperating with team and possibly intentionally feeding". But then, all of a sudden, this cassiopeia, who is probably queued with this renekton based off how strongly she defends him, is like "STFU Amumu you cant report him for this".

So, At the end of the game, I still report him. But my team also reports me because they think im trying to flame the renekton by saying to report him?

So im wondering, is the thing that the renekton doing reportable? Also, is the thing that Im doing reportable?

Thank you!

~Boompenguins