While a good argument can be made in favor of dealing with the loud music til you get your gas and just getting out of there (which is what I'd have done) your analogy isn't quite right.
See, the EXPECTED result of walking into a puddle is getting wet. The expected result of telling some kids to turn down their music is not to have your life threatened. At least, it has not traditionally been. It has traditionally been, back when kids had respect for adults... to be heeded. More recently, it was to be mocked and ignored. Being threatened with death, as this man describes, is a new frontier in adult/teen interactions.
By no means am I certain that what he claims happened actually did, but I do strongly suspect something happened to make him shoot that gun, other than just whim and other than just not being heeded, or being mocked.
I could be wrong, but I find it hard to believe this man would flush his life down the toilet and attempt to take the lives of strangers because they wouldn't turn their music down. I don't buy it.