The tutorial says:
"EDIT: Be sure you are on a server that contains the following plugins: FAWE, FAVS and BetterBrushes!"
I looked up BetterBrushes, and it seems to just re-add the better versions of the Voxel erosion brushes that existed before the 1.11.2 update. This would be super useful, since the current erosion brushes suck ass (they're exactly identical to WE adjacency mask with different parameters anyways). However, it doesn't look like there's even a reliable download page for BetterBrushes anywhere.