It's harmless
It's just a small glitch in MacOS. It really can't be exploited by anyone much. A true Mac user would never accidentally type 'root' as a user name. And look at all the flaws in windows. One tiny flaw in Apple is nothing by comparison. I'd sooner use my Mac any day than Windows.
Seriously though, I *DO* use a mac, I do prefer using it, but for fucks sake Apple! This is TERRIBLE!!! Very poor show....