No doubt. If it would be if anyone I would think it would be Shuri. Her picture just struck me as looking like QDJ.
Indeed, I immediately thought QDJ at first.
The IG post from her agent isn't a 100% confirmation, but I seriously doubt he would use a post that has Shuri's picture randomly like that.
Unless he's trying to misdirect people...which is kinda silly, as he could've simply posted something that didn't have a specific character that wasn't casted yet.