I don't see that the bus was knocked over. In the photos, the bus is upright and there was no mention of it tipping. It got pushed off the road, and a power pole was knocked over.

Each accident is different. The wreckage of the SUV doesn't look like it hit all that hard. It struck the left front corner of the bus. In doing so it may have pushed the wheel, or caused the driver/steering wheel to move sideways. Either could cause the bus to briefly drive itself off the road more so than being directly pushed by the SUV. The bus does seem to have been moving at the time of impact.

That depends, batteries on top might make it top heavy and much more likely to roll over...

I just saw a video of a man who was rescued by police from a burning vehicle. He suffered a medical incident while back his truck up and ended up flooring the gas as he got into his parking spot. The tires spun high speed while the truck stood still until they caught fire and almost burned him alive. He did suffer smoke inhalation but I believe made it. It could have been the bus driver attempting to make evasive maneuvers added to the fact the car hit it as well could be why it ended up a bit farther off the road then expected.

Don't worry, the SUV driver is going to get what's coming to them from the government