To be fair,
Sticking a mortar into a bottle is childish behavior.....I mean, seriously.
Also to be fair, you lit 15 feet of dry grass on fire, hence the anger, I mean, that could have seriously and easily gone out of hand
From the post, it sounds like you didin't do this on your own property, or a property owned by one of your friends, which also makes it illegal, especially without supervision of police
To me, it sounds like you are highly immature.