Like a lot of things, that depends on exposure and concentration. Uncontrolled exposure from concentrated acid delivered via ventilation systems could easily end up on the higher end of the scale, even ignoring second order effects like an unplanned evacuation of a building surrounded by protests. The acid has a '3' for health effects (and a '2' for flammability).
Very hazardous in case of skin contact (irritant), of ingestion. Hazardous in case of eye contact (irritant), of inhalation. Slightly hazardous in case of skin contact (corrosive, permeator). Liquid or spray mist may produce tissue damage particularly on mucous membranes of eyes, mouth and respiratory tract. Skin contact may produce burns. Inhalation of the spray mist may produce severe irritation of respiratory tract, characterized by coughing, choking, or shortness of breath.
Potential Chronic Health Effects:
The substance is toxic to lungs, the nervous system, mucous membranes. Repeated or prolonged exposure to the substance can produce target organs damage. Repeated or prolonged contact with spray mist may produce chronic eye irritation and severe skin irritation. Repeated or prolonged exposure to spray mist may produce respiratory tract irritation leading to frequent attacks of bronchial infection.
For this kind of chemical compounds it's very important to consider the concentration before getting scared.
If you put a 5% of acetic acid in water, you essentially get vinegar. No one is afraid of vinegar and it has almost no health risks. I think it would be not a good idea to put your head in a bathtub full of vinegar. (I never tried.) But vinegar is safe enough to use it to rinse your hair, drop it in your hands and drink a small amount of it. (Just don't put it in your eyes!)
I worked a few decades ago with acetic acid 100% a few times. For historical reasons it's called Glacial Acetic Acid. Very nasty stuff. If someone opens a bottle the smell is so strong that it will make you weep in spite you are a few foots away. It's better to open it only in a fume hood, or something that keeps the smell away. I never tried to touch it. I think that if you touch it and wash immediately there are no risk, perhaps a small rush. But definitely keep it far away from the eyes and nose.
I agree with the sibling comment that it was more a stinky bomb that something designed to kill someone. Anyway, the police should stop them, but without exaggerating the risks. For example in a recent soccer math in Argentina one of the spectators throw some kind of homemade pepper spray to the players of the other team. It was too strong and a few payers had to go to the hospital. Autotranslation: https://translate.google.com.ar/translate?sl=auto&tl=en&js=y...
I agree, it was probably not intended to kill anyone. I don't agree that it couldn't have. People could have been trampled during evacuation, someone could have already had respiratory ailments, etc.
Motive aside, even if it could have killed ten people by downplaying that risk the terrorists lose.
It's kind of like how sending suicide bombers to Israel is pretty much futile. The populace knows that unless they come by the hundreds of thousands it's not a risk worth being scared of. You can't terrorize people who don't think you're scary.
Me, I would have picked butanethiol.
But my first thought, reading "dumping acid", was LSD ;)