Since you asked...Anyhow, watch the last 1 minute of the video and maybe someone can tell me how not to go down like I did.
I'll say I'm probably the least experienced and knowledgeable out of those replying, but that's not going to stop me from throwing out some wild speculation!
It seemed like you might have been holding your clutch and then gave it a good dose of throttle and came off the clutch quickly while at a bit of an angle, causing the back wheel to break loose. And instead of sensing that and reducing throttle a fuzz to get it back in line, you stayed in it, sending the back end around on you.
It sounded like you did the same thing in the washboard turn section a few moments earlier in the video, just this time it was enough throttle/angle to cause a problem.