This is normal. It occurs when a straight-line mission is loaded into DJI Fly. DJI Fly can only create a curved turn mission. A straight-line mission can be externally created, loaded, and executed with DJI Fly. It just looks wonky as you have...
That would be the altitude of the POI with respect to your take-off location. It is used to calculate the gimbal pitch angle so that the POI is centered vertically in the view of the camera
You are expected to estimate the altitude of the POI...