I looked into this myself.
To be banned for 4 weeks you would have had to have done some pretty egregious stuff or been banned many previous times. In this case, you have 3 previous unsportsmanlike conduct bans for own-goaling. This most recent unsportsmanlike conduct ban was for AFKing.
As your next ban is likely to be perma, I would recommend two things:
1. Turn off chat (since you have a pretty extensive history there as well)
2. Try to remember your teammates are people too. It's easy to get tilted, but people make mistakes. No need to grief and try to ruin other's good time
EDIT: I just want to also say that this is another example of our new system issuing Unsportsmanlike Conduct bans, which works on a combination of gameplay analysis and user reports. The system only works when you report, so please continue to help us help you by reporting cases like these.