There are too many sources of shared air for smoke to stay contained within one unit.
Vents are not the only cause of contamination. Aggravating amounts of smoke can easily passes through pipes, floorboards, and even walls.
Even if the smoker opens the windows or smokes on the balcony, the smoke drifts to the other units through the outside air, preventing the non-smoking tenants from open their windows without exposure to smoke.
Non-smoking tenants with or without a pre-standing ailment, such as asthma or a heart condition among others, can become medically ill from the exposure.