Some driving terms cross over from motorcycles to cars. One of those is highside. A highside is generally preceded by a lowside. The high and low describe which side of the bike you fall off of (which is why I don’t ride a motorcycle).
If you’re going around a corner in a car and the rear suddenly loses traction, you get oversteer, and a spin. On a motorcycle, the bike slips away and the rider falls on the ground. This is a lowside. The distance might not be very far, but a high speed crash has to suck no matter how far you fall. The causes of a lowside are what you expect: mid-corner braking, power oversteer, oil, etc.
The correction for oversteer in a car is to countersteer. Perfectly executed, the rear of the car steps out and steps right back into line. But if the steering lock is held too long, the rear slingshots back to the other side, possibly making matters worse. The highside is analogous to this situation. In an attempt to recover a lowside, a rider may regain too much grip. This can violently slingshot the rider over the high side of the bike.
Did you see/hear the rider whack open the throttle just before the incident? That caused the rear of the bike to slip away and enter a lowside. As the rear came around it regained traction and flipped the bike and rider. Double ouch.
No, this blog didn’t suddenly become yousuckatmotorcycling. It’s rare, but a car can also highside with a sudden change in direction. It helps if the car has a high center of gravity and hits a berm.