I got a Ring of Emptyness (WD) on my demon hunter. I somehow feel as if the thing is bugged, never seen a non-class primal drop before
It's no bug.
"upon completing your first Greater Rift 70 or higher Solo, you’ll receive an achievement indicating your accomplishment and the Greater Rift boss will be guaranteed to drop a Primal Legendary. This drop is subject to all other loot rules—meaning while there’s a large chance it will be suited for your class, randomness does play a factor." https://www.diablofans.com/news/49083-season-16-the-season-of-grandeur-begins-1-18