The frame of reference was lined up in the beginning of the video before the camera moved up. It was the distance from the hoop to the gym floor.
The projectile height is the height that the ball is released from the shooters hands. The projectile height could change if this was a jump shot because you are still measuring from the floor to where the ball is leaving his hands.

The projection angle or take-off angle is the angle that the ball is realeased from the shooters hand. This is one of the factors that affects the motion of a projectile. The angle being above 45 degrees indicates that the shooter is more concerned about increasing projection height rather than projection distance.

The maximum velocity is occuring between the greatest height of the ball and the height of the ball where it was released. Maximum velocity is going to be occurring mid movement.

During projectile motion gravity is acting on the ball and pulling it down towards the ground at 9.8 m/s^2
The trajectory can be broken up into a vertical and horizontal velocity component and can be used to determine the angle of the travejctory. The vertical component will only go up until the ball reaches the highest point.

At maximum height duing projectile motion, the velocity is equal to zero. It is no longer traveling up or traveling down.

Zero velocity occurs when the ball is changing directions from traving up to traveling down.

As the ball begins to fall and travel towards the hoop, the vertical velocity component goes in the direction of gravity and the trajectory is now down towards the hoop. The horizontal velocity component remains constant.