Thanks for the response. It's highly doubtful that happened suddenly resulting from the crash. Takes time to get that kind of build-up.
You mentioned a lot of stop & go riding; did you get much highway riding? That kind of build up could occur if you spend a lot of time idling and rolling around at low-rpm. If that's the case, it's never a bad idea to take her out on the highway once in a while to blow a little carbon off. (aka Italian tune-up.)
of your pistons look like that? Any oil consumption? A leaky valve seal could cause that kind of build up. But it's highly unlikely all four cylinders would have a leaky valve guide seal in so few miles.
Glad you're okay. Any time you can walk away from a totalled bike, you drink a toast to your own good fortune.