The other guys have clarified how it was an account ban, so I won't go into that. But I will say that the professional players and other high-elo streamers, in some respects, are held to even higher standards than the rest of the League community because of the amount of exposure they get. Hear me out. Yes, many of them can be utter jerks on stream, but many of them keep the rage and trash talk verbal, so that only their stream or duo partners can hear it, and rarely type any of it in chat.
Something else to keep in mind is that the decision to actually dispense a punishment to an account is based upon the severity of the infraction and the consistency of rule-breaking. Another way to look at that is in what percentage of games is a player being toxic. For a recreational player, they may only play a handful of games a week and 1-2 toxic games can be a significant percentage. Many professional players and streamers play more games in a single day than the average player plays in a week. Having 1-2 mildly toxic games for them won't amount to anywhere near as high of a percentage. That doesn't mean that the pros can get away with being toxic more often though. Riot has said many times that they try not to punish players for having a bad day, provided that they are not excessively negative/toxic. Just to give an example, if you've ever watched BoxBox, he is probably one of the nicest guys I've ever seen stream. I have literally never seen him flame or rage at anyone, and I've been subbed to him for 2.5 years. If he were to have a really bad day, and just rawr a bit, and have some minor flaming (like... omg you guys suck, report x9, where'd you buy your account... those kinds of things, not hate speech or kys types of things) it probably would not result in him being punished. It would be flagged in the system, and would be marked on his account, so that if he continued to do so, he would end up being punished for it, but a first instance of it compared to the thousands of positive games he has would likely not result in corrective action. So it isn't that the pros don't get punished, it's just that they often have such a minor percentage of negative behavior compared to an overwhelming percentage of positive/neutral behavior.
Another difference with the pro players/high-elo streamers that leads me to say they are held to higher standards in some regards has to do with the Player ban, as opposed to an Account ban. I've actually never met or even seen a thread here dealing with a player that was not a professional who was given a lifetime/player ban. The only ones I can think of off the top of my head are Jensen and Tyler1. You never hear about RandomLeaguePlayerXX1 having his accounts banned on sight. No, you hear about these pro players who have thousands of fans trying to emulate. It's fine when that means everyone wants to try and xPeke. It's not fine when everyone wants to run it down mid. So where RandomLeaguePlayerXX1 would just get his next smurf banned, pro players can get themselves banned.