THe Update is from last week friday to be exact .
It even says in the blue post that only Head , shoulders , chest , hands and legs go towards the set bonuses . You have to learn how to read beyond 1 paragraph (the top one)
At a base level, how it works is you input a piece of Season 3 gear and a corresponding tier set piece will be made with a matching item level. The useable items can be Season 3 gear from raids, Mythic+, PvP, World Boss Antros, or items purchased with Sandworn Relics from Rafiq in Pilgrim’s Grace, Zereth Mortis. The applicable slots are helms, shoulders, cloaks, chests, bracers, gloves, belts, legs, and boots.. Note that the 2-piece and 4-piece set bonuses will only be on the helms, shoulders, chests, gloves, and legs.