Generally they end up flying low during the air show so they can be seen more easily. They would practice high yo start with and then bring the stunt lower and lower to get a better feel for how it would work lower to the ground consistent with what they will be doing at the airshow.

It is likely this was one of the ones that was the same or close to the altitude they would be doing the stunt at during the airshow.

Pretty sure they usually are. Training usually has a "hard deck" that they're supposed to treat as the ground, and if they go past it they "die". I wonder if this pilot blacked out mid maneuver