same thing happened to me although it was on a honda 250 in thailand. I had hired the bike and ridden most of the day on fast sweeping roads I was cutting through a rain forest on a dirt track and one second i am merrily ridding along next i am in the dirt with a bad knee.

I couldnt understand what had happened then i found the brake caliper had come loose and locked the front wheel.

Luckily i had a leatherman and I was able to cut some wire from a fence to back up my cable tie.

I'm just glad it happened at 25-30 kph and not over 100 kph

I actually carried on for 2 more days of great roads and trail with no problems and just returned the bike after dark