The irony that we can discuss in detail what we would've done in this scenario based on video evidence provided by these apparently so-called fools and their trigger-happy fingers is very amusing.
Let me repeat what happened. Some guy threw a Molotov cocktail in a crowded train. Most people got out safely, some experienced burns, and the main perpetrator caught his pants on fire. Overall, everyone stayed calm in this whole scenario, which is great because the danger of a stampede is always a possibility in Hong Kong. The last thing one needs is amateur heroes running around indiscriminately spraying around fire extinguishers in a cabin that's already deprived of oxygen and shouting at everyone to get the hell out.