His bottom line "when you find #000000 in your color picker, ask yourself if you really want pure black. You’re probably better off with something more natural. And if you’re feeling adventurous, try staying away from the left edge of the color picker altogether" is much less radical than his title "never use black".

I think this more subtle statement is fair advice to beginners in design, who might sometimes make an unreflected choice of black or not be aware that shadows aren't just black.

So in my opinion it's probably bad advice for more experienced artists like you, but it might be very helpful advice for somebody else.