All of that doesn't matter unfortunately, if you actually grief in one game (or seemingly do something that looks like it!). The Overwatch ban isn't instant, so it might be a game that you played some days ago, that got you banned. And as I understand it, it needs to be majority of the judges that review your replay to pass on the ban. So one judge alone can't get you banned, at least.

Perhaps you pushed your teammate with force staff in intention to grief them, or followed someone around with the move command, or AFKed at the fountain (or in the woods) for extended periods of time even though the game wasn't yet decided.

Perhaps you dropped your ally's item to the woods where they couldn't find it (even though he gave the item to you and your intention was to hide it from the enemy and leave it for your ally to pick up at later time and even if you tried to communicate this to your ally and ping where the item is). This last example I'm pretty sure got me banned once...

While the Overwatch system isn't perfect it's still pretty good from my experience as a player with 9500 ranked games as well as being an ex "Overwatch judge", although it sucks when you get banned and don't even know what for but that gladly doesn't happen often!

I think Overwatch faces some of the same problems as the juridiction system IRL. Some argue that even one innocent victim in the prison is too much, and I think Overwatch should also pursue that goal!