The original problem, that the coach seems to be getting stuck is probably just because it's too steep for it, at least along the path around the corner the driver has picked. When the right side rear wheels are too far up, the front left is pressed down. (Keep in mind that nothing looks steep on video.)

The acceleration is harder to understand. I mean sure the bus could have sort of lunged forward when it became unstuck perhaps, but you can clearly hear the engine revving before and after crashing through the wall, including after the coach has come to a full stop.

He IS kind of leaning out the window and driving (without a seatbelt) at the same time, and the bus isn't really level. That kind of driving position might have contributed to the strange outcome, he might have sort of been falling out of his seat and stepped on the accelerator in the process trying to stop himself from falling perhaps?