I agree that it was inappropriate of the person to smoke, it would have irked me, and it was very appropriate you said something. But it's sounds like you overstated your case. Merideth is right. The exhaust from the tailpipes would be worse, especially for diesel vehicles. And parents seem to idle a lot when picking up/dropping off kids (see note at bottom why this is bad).
Are there more asthmatic kiddos on special needs campuses than regular school campuses? I can only think of asthmatic kiddos who might be more threatened by smoke, and I think asthmatic kids are not considered "special needs". I'm unaware of how other special needs kiddos would be particularly sensitive (or more delicate in your words) to a whiff of smoke (or tailpipe exhaust for that matter). And I'm not being facetious. I am truly unaware of why children on a Special Needs campus would be more sensitive to air pollutants. I'm happy to learn otherwise, but please withhold the invective.
Somewhat off topic but informative regarding air pollution:
For those who are interested in vehicular pollution, cars emit greater amounts of pollutants while idling than when moving. When conducting traffic air quality studies, the areas of focus are signalized intersections near where the cars are stopped/idling. It's not because the cars are stationary, but because the vehicles emit much larger quantities of pollutants when idling or traveling at very slow speeds. Idling vehicles really do pollute. Unless it's diesel, the primary pollutant is carbon monoxide, which you can't smell.
And, if you're still with me... For those of you who live in areas where there are a lot of wood-burning stoves (or simply a lot of folks who like to have a wood fire in the fireplace), those are the all-time worst air pollution offenders. Generally worse than vehicles and industry, with a bunch of small particulate matter.