Do not worry too much about the Report notification… as long as you are innocent…
Feel free to PM Game Masters in Game or here on our Forum if you have concerns about being reported, and they can explain things
Never Team Kill tho… it can be reported as malicious behavior and that can lead to Account ban…
There is a technical automated system in game for taking TKs into account, as others pointed out… it can kick you out of a match, or it can have increasing time out punishments… may also lead to Account bans as well in the end
So, best not to risk it… not sure if it is the same for custom matches tho… so best to check with Game Masters in any case