You've never lived in a Mexican area. I used to live in Oceanside Ca. and every new years and fourth of July it sounded like a firefight in Vietnam. I mentioned this to a city council member and she said she would put on a hard hat and get in her bathtub. true It's a "cultural" thing.
I used to live in a very Hispanic part of Houston, by Hispanic i mean Mexican.

I heard gunshots on a weekly basis, just vatos getting drunk and shooting in the air.
Cinco de mayo was a riot, you would hear people shooting into the air 10-20 shots at a time.
The cops never really could track it down, shooting into the air makes it hard to locate.
Was dating this Mexica broad back then, i went to her families house on NYE. Her drunk uncle would just fire off his 9mm into the ground randomly. Nobody made a big deal about it.
Apparently in Mexico, depending on which area, this is very common for celebration.