Pretty simple, if you're pleading ignorance and I believe you, you can't just assume any black guy is a ghetto black. Dude had just logged in 5 minutes prior to you killing him. So obviously you need to make sure that he's the right guy and you can't just blindly listen to someone. Per these rules
You killed him after the second hit and in the sit insinuated that he may have 'bled out'.
Your ban record shows 4 past RDM bans / notes from this year and 2 from last year. With a warn for RDM as recently as June 17th (Yesterday). You seem to be consistently ignoring the rules as you continue to get banned, likely inserting yourself in situations you don't belong in for free kills.