The question isn't if they breathe, it states they breathe, the question is does toxic gasses and other things that can be inhaled hurtful to them since they are artificial beings like constructs? Can they drown, or do they not need oxygen to survive since they are a completely artificial humanoid?
Think of androids like in Alien or even Data on Star Trek: Next Generations, completely artificial, act like humans and eat, drink, and breathe like them, but are not affected by the atmosphere and toxic gasses that affect humans, because their organs are artificial.