I have been banned before for this, although I seem to have just managed to kill 12 teammates in one go. Just live a day without WT, also I think it probably is the teamkilling after match ends, or even just a couple here and there.
You can kill ypur team with air weapons…both aircraft and tanks
You can kill your team with artillery
Additionally (probably not the case here) you can kill your team by pushing them into rivers or enemy fire. This last one is not automatic…requires a complaint.