An in universe answer to go with what the director/writers/other intended: when any of the snaps happened the wielder of the stones was not expressing exactly what would happen to every individual in the universe, but was concentrating on an overall intention which the stones read, interpreted, and bent the universe to implement.
Thanos didn't specify in detail which life to take, he may not have specified the dusting organisms in any way, just "half of all sentient life is to go".
Similarly, Smart Hulk probably just thought something along the lines of "bring everyone who went back safely", and the stones interpreted that intent, bringing most back to exactly where they were (presumably the least complicated path) and those who would not be safe to a similar but different point (standing on the deck of a different plane, or on the lap of the person in the equivalent seat, or at one of the airports on their journey, for in-flight examples).
Of course that still leaves some questions and problems: what about those killed indirectly by the snap, those hit by suddenly driver-less cars and so forth (I assume they are still gone, though there is nothing stated in the films to support either way) and there would be complications with such as planes suddenly being over their designed carrying capacity. I doubt Hulk's snap was perfect.