Yes, a withdrawal settlement is different from a lump-sum. A withdrawal settlement extinguishes all other rights to any other future benefits.
Any retiree who elects to receive a benefit under Article 28 (Retirement benefit) or Article 29 (Early Retirement Benefit) has an option to partially commute their benefit into a lump-sum up to a maximum of 1/3 the actuarial equivalent of such benefit to be paid upon separation from service and the balance to be paid as a reduced monthly pension.