Glad you're not hurt.
As a side note, I've used smoke grenades when paintballing - pretty harmless but you can't see nowt apart from a bright pink cloud. Still, if I saw that come through my letter box I would instantly think firework too.
The thing is, is that when I was a kid I wouldn't even dream of chalking on the pavement, let alone doing stuff like this. Its all down to the parents and upbringing - scummers will bring up even more scum. If you have good parents and get told from and early age to respect your fellow man then things like this won't happen.
Chavs and scum like this are the plague of this earth in my opinion. They contribute diddle s*** yet leach from the system, they pick fights, cause arguments, shout 24/7, thick as two short planks, no drive to better themselves, etc, etc - I have literally no time for them.