Shimano BR-T4000 not compatible with frame pivot stud
Nothing is wrong here, just put the brake arms on and torque down the bolts. Your old brake arms are the type that pivot directly on the stud, and the new ones are the type that overhang the stud and have an integral pivot of their own. Use more torque than you would on the other type, because with integral pivots there's no risk of mushrooming the stud.