Wondering about the ban system?

I'm not a very toxic community member, if I have something to say I usually keep to myself. And if the enemy team has something salty or rude to say I just usually reply with "k" or "idc"

One of my friends have gotten banned for 8 months already, when they first got the account they were extremely toxic but it became a very watered down version after a while. He isn't usually toxic anymore actually, but when he got banned he exploded at one of his teammates and it just became 2 dogs neck and neck with each other.

Did he get banned for that one toxic game or for the continuous streams of reports and toxicity from his past and that game just so happened to tick everything off balance?