Thanks for the question!
They’re referring to using cocoa powder to add contrast to your latte art. When you do latte art you should be using the color from the espresso, and (typically) free pouring to create the design, using your wrist and such to create the patterns. There’s a technique that allows the “art” to stand out in the coffee cup, with the natural contrast from that and the espresso.
If you use cocoa powder, you’re adding contrast and with cocoa powder is a lot easier to make latte art because you don’t have to have the pour technique down perfect - you just have to be able to swirl a spoon in the foam/powder to make a basic swirl and such.
So, the main debate is - should it count when you’re looking at good latte art? Like one person said - if the talent is all ready there, your mochas can look awesome!