When people say "chemical weapon" they think "weapon of mass destruction" even if they don't know names like mustard gas, vx or seran. These are clearly very different categories of things.
It sucks that this will get a pass from many people when they realize schoolkids weren't at risk of mass death, because teargas simply isn't going to kill a lot of kids. Should the cops have behaved better? Yes. Should they be in trouble for tear gassing kids? Yes. Will this be downplayed while people argue uselessly if this was or wasn't a chemical weapon attack while trying to get a better understanding of the story? Yes. Will this water down future talks of weapons of mass destruction as "Chemincal Weapons"? I think it will.