Yes. You are liable for damages. You set the dangerous uncontrollable force into motion and your are liable for the consequences.
The owner of the car did nothing wrong. By parking the car in a public street, they did not bargain for having the vehicle become a landing zone for fireworks.
My advice: Pay their damages or risk a judge awarding that plus court costs and more.
\This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.