I have noticed small displacements from the vertical in my own videos. Usually they are of the order of millimeter or smaller but apparently they seem to show a large discrepancy with the expected behaviour.
I attributed then to: (i) problems of alignment of the camera (your image seems to be taken from the floor) an the trajectory maybe slightly distorted, (ii) unintentionally given the object a moment in the x-direction. In the first case, you may use a camera tripod.
This is a perspective view, the z axis of the camera is not perpendicular to the plane and your camera is rotated around this z axis. The output is consistent with the data you entered.
